diff --git a/src/main/java/stirling/software/SPDF/config/security/UserService.java b/src/main/java/stirling/software/SPDF/config/security/UserService.java
index 60b3ebef..666baa93 100644
--- a/src/main/java/stirling/software/SPDF/config/security/UserService.java
+++ b/src/main/java/stirling/software/SPDF/config/security/UserService.java
@@ -176,6 +176,10 @@ public class UserService implements UserServiceInterface {
         return userRepository.findByUsername(username);
     }
 
+    public Optional<User> findByUsernameIgnoreCase(String username) {
+        return userRepository.findByUsernameIgnoreCase(username);
+    }
+
     public void changeUsername(User user, String newUsername) {
         user.setUsername(newUsername);
         userRepository.save(user);
@@ -194,4 +198,8 @@ public class UserService implements UserServiceInterface {
     public boolean isPasswordCorrect(User user, String currentPassword) {
         return passwordEncoder.matches(currentPassword, user.getPassword());
     }
+
+    public boolean isUsernameValid(String username) {
+        return username.matches("[a-zA-Z0-9]+");
+    }
 }
diff --git a/src/main/java/stirling/software/SPDF/controller/api/UserController.java b/src/main/java/stirling/software/SPDF/controller/api/UserController.java
index 07c4b934..e5c0b114 100644
--- a/src/main/java/stirling/software/SPDF/controller/api/UserController.java
+++ b/src/main/java/stirling/software/SPDF/controller/api/UserController.java
@@ -61,11 +61,16 @@ public class UserController {
             HttpServletRequest request,
             HttpServletResponse response,
             RedirectAttributes redirectAttributes) {
+
+        if (!userService.isUsernameValid(newUsername)) {
+            return new RedirectView("/account?messageType=invalidUsername");
+        }
+
         if (principal == null) {
             return new RedirectView("/account?messageType=notAuthenticated");
         }
 
-        Optional<User> userOpt = userService.findByUsername(principal.getName());
+        Optional<User> userOpt = userService.findByUsernameIgnoreCase(principal.getName());
 
         if (userOpt == null || userOpt.isEmpty()) {
             return new RedirectView("/account?messageType=userNotFound");
@@ -73,6 +78,10 @@ public class UserController {
 
         User user = userOpt.get();
 
+        if (user.getUsername().equals(newUsername)) {
+            return new RedirectView("/account?messageType=usernameExists");
+        }
+
         if (!userService.isPasswordCorrect(user, currentPassword)) {
             return new RedirectView("/account?messageType=incorrectPassword");
         }
@@ -186,6 +195,18 @@ public class UserController {
             @RequestParam(name = "forceChange", required = false, defaultValue = "false")
                     boolean forceChange) {
 
+        if (!userService.isUsernameValid(username)) {
+            return new RedirectView("/addUsers?messageType=invalidUsername");
+        }
+
+        Optional<User> userOpt = userService.findByUsernameIgnoreCase(username);
+
+        if (userOpt.isPresent()) {
+            User user = userOpt.get();
+            if (user != null && user.getUsername().equalsIgnoreCase(username)) {
+                return new RedirectView("/addUsers?messageType=usernameExists");
+            }
+        }
         if (userService.usernameExists(username)) {
             return new RedirectView("/addUsers?messageType=usernameExists");
         }
diff --git a/src/main/java/stirling/software/SPDF/repository/UserRepository.java b/src/main/java/stirling/software/SPDF/repository/UserRepository.java
index d63c4cba..faa11fcc 100644
--- a/src/main/java/stirling/software/SPDF/repository/UserRepository.java
+++ b/src/main/java/stirling/software/SPDF/repository/UserRepository.java
@@ -3,10 +3,14 @@ package stirling.software.SPDF.repository;
 import java.util.Optional;
 
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
+import org.springframework.data.repository.query.Param;
 
 import stirling.software.SPDF.model.User;
 
 public interface UserRepository extends JpaRepository<User, String> {
+    Optional<User> findByUsernameIgnoreCase(String username);
+
     Optional<User> findByUsername(String username);
 
     User findByApiKey(String apiKey);
diff --git a/src/main/resources/messages_ar_AR.properties b/src/main/resources/messages_ar_AR.properties
index aef98de5..63a459a4 100644
--- a/src/main/resources/messages_ar_AR.properties
+++ b/src/main/resources/messages_ar_AR.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=User not authenticated.
 userNotFoundMessage=User not found.
 incorrectPasswordMessage=Current password is incorrect.
 usernameExistsMessage=New Username already exists.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Admin User Control Settings
 adminUserSettings.admin=Admin
 adminUserSettings.user=User
 adminUserSettings.addUser=Add New User
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Roles
 adminUserSettings.role=Role
 adminUserSettings.actions=Actions
diff --git a/src/main/resources/messages_bg_BG.properties b/src/main/resources/messages_bg_BG.properties
index f85f53cc..4428a68b 100644
--- a/src/main/resources/messages_bg_BG.properties
+++ b/src/main/resources/messages_bg_BG.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=Потребителят не е автентикира
 userNotFoundMessage=Потребителят не е намерен
 incorrectPasswordMessage=Текущата парола е неправилна.
 usernameExistsMessage=Новият потребител вече съществува.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Настройки за администраторск
 adminUserSettings.admin=Администратор
 adminUserSettings.user=Потребител
 adminUserSettings.addUser=Добавяне на нов потребител
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Роли
 adminUserSettings.role=Роля
 adminUserSettings.actions=Действия
diff --git a/src/main/resources/messages_ca_CA.properties b/src/main/resources/messages_ca_CA.properties
index e76b5b4d..a97f6604 100644
--- a/src/main/resources/messages_ca_CA.properties
+++ b/src/main/resources/messages_ca_CA.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=User not authenticated.
 userNotFoundMessage=User not found.
 incorrectPasswordMessage=Current password is incorrect.
 usernameExistsMessage=New Username already exists.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Usuari Admin Opcions Control
 adminUserSettings.admin=Admin
 adminUserSettings.user=Usuari
 adminUserSettings.addUser=Afegir Usuari
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Rols
 adminUserSettings.role=Rol
 adminUserSettings.actions=Accions
diff --git a/src/main/resources/messages_de_DE.properties b/src/main/resources/messages_de_DE.properties
index 7a783db5..3340a306 100644
--- a/src/main/resources/messages_de_DE.properties
+++ b/src/main/resources/messages_de_DE.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=Benutzer nicht authentifiziert.
 userNotFoundMessage=Benutzer nicht gefunden.
 incorrectPasswordMessage=Das Passwort ist falsch.
 usernameExistsMessage=Neuer Benutzername existiert bereits.
+invalidUsernameMessage=Ungültiger Benutzername. Der Benutzername darf nur Buchstaben und Zahlen enthalten.
 deleteCurrentUserMessage=Der aktuell angemeldete Benutzer kann nicht gelöscht werden.
 deleteUsernameExistsMessage=Der Benutzername existiert nicht und kann nicht gelöscht werden.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Administrator-Benutzerkontrolle
 adminUserSettings.admin=Admin
 adminUserSettings.user=Benutzer
 adminUserSettings.addUser=Neuen Benutzer hinzufügen
+adminUserSettings.usernameInfo=Der Benutzername darf nur Buchstaben und Zahlen enthalten, keine Leerzeichen oder Sonderzeichen.
 adminUserSettings.roles=Rollen
 adminUserSettings.role=Rolle
 adminUserSettings.actions=Aktion
@@ -416,7 +418,7 @@ login.title=Anmelden
 login.header=Anmelden
 login.signin=Anmelden
 login.rememberme=Angemeldet bleiben
-login.invalid=Ungültiger Benutzername oder Passwort.
+login.invalid=Benutzername oder Passwort ungültig.
 login.locked=Ihr Konto wurde gesperrt.
 login.signinTitle=Bitte melden Sie sich an
 
diff --git a/src/main/resources/messages_el_GR.properties b/src/main/resources/messages_el_GR.properties
index 8f96f8b8..b3531514 100644
--- a/src/main/resources/messages_el_GR.properties
+++ b/src/main/resources/messages_el_GR.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=\u039F \u03C7\u03C1\u03AE\u03C3\u03C4\u03B7\u03C2 \u03B4
 userNotFoundMessage=\u039F \u03C7\u03C1\u03AE\u03C3\u03C4\u03B7\u03C2 \u03B4\u03B5\u03BD \u03B2\u03C1\u03AD\u03B8\u03B7\u03BA\u03B5.
 incorrectPasswordMessage=\u039F \u03C4\u03C1\u03AD\u03C7\u03C9\u03BD \u03BA\u03C9\u03B4\u03B9\u03BA\u03CC\u03C2 \u03C0\u03C1\u03CC\u03C3\u03B2\u03B1\u03C3\u03B7\u03C2 \u03B5\u03AF\u03BD\u03B1\u03B9 \u03BB\u03B1\u03BD\u03B8\u03B1\u03C3\u03BC\u03AD\u03BD\u03BF\u03C2.
 usernameExistsMessage=\u03A4\u03BF \u03BD\u03AD\u03BF \u03CC\u03BD\u03BF\u03BC\u03B1 \u03C7\u03C1\u03AE\u03C3\u03C4\u03B7 \u03C5\u03C0\u03AC\u03C1\u03C7\u03B5\u03B9 \u03AE\u03B4\u03B7.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=\u03A1\u03C5\u03B8\u03BC\u03AF\u03C3\u03B5\u03B9\u03C2
 adminUserSettings.admin=\u0394\u03B9\u03B1\u03C7\u03B5\u03B9\u03C1\u03B9\u03C3\u03C4\u03AE\u03C2
 adminUserSettings.user=\u03A7\u03C1\u03AE\u03C3\u03C4\u03B7\u03C2
 adminUserSettings.addUser=\u03A0\u03C1\u03BF\u03C3\u03B8\u03AE\u03BA\u03B7 \u03BD\u03AD\u03BF\u03C5 \u03A7\u03C1\u03AE\u03C3\u03C4\u03B7
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=\u03A1\u03CC\u03BB\u03BF\u03B9
 adminUserSettings.role=\u03A1\u03CC\u03BB\u03BF\u03C2
 adminUserSettings.actions=\u0395\u03BD\u03AD\u03C1\u03B3\u03B5\u03B9\u03B5\u03C2
diff --git a/src/main/resources/messages_en_GB.properties b/src/main/resources/messages_en_GB.properties
index 3f982b2d..41c9f30a 100644
--- a/src/main/resources/messages_en_GB.properties
+++ b/src/main/resources/messages_en_GB.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=User not authenticated.
 userNotFoundMessage=User not found.
 incorrectPasswordMessage=Current password is incorrect.
 usernameExistsMessage=New Username already exists.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Admin User Control Settings
 adminUserSettings.admin=Admin
 adminUserSettings.user=User
 adminUserSettings.addUser=Add New User
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Roles
 adminUserSettings.role=Role
 adminUserSettings.actions=Actions
diff --git a/src/main/resources/messages_en_US.properties b/src/main/resources/messages_en_US.properties
index e430630a..2d7524f5 100644
--- a/src/main/resources/messages_en_US.properties
+++ b/src/main/resources/messages_en_US.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=User not authenticated.
 userNotFoundMessage=User not found.
 incorrectPasswordMessage=Current password is incorrect.
 usernameExistsMessage=New Username already exists.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Admin User Control Settings
 adminUserSettings.admin=Admin
 adminUserSettings.user=User
 adminUserSettings.addUser=Add New User
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Roles
 adminUserSettings.role=Role
 adminUserSettings.actions=Actions
diff --git a/src/main/resources/messages_es_ES.properties b/src/main/resources/messages_es_ES.properties
index 9be5f90a..adaab7de 100644
--- a/src/main/resources/messages_es_ES.properties
+++ b/src/main/resources/messages_es_ES.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=Usuario no autentificado.
 userNotFoundMessage=Usuario no encontrado.
 incorrectPasswordMessage=La contraseña actual no es correcta.
 usernameExistsMessage=El nuevo nombre de usuario está en uso.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Configuración de control de usuario administrador
 adminUserSettings.admin=Administrador
 adminUserSettings.user=Usuario
 adminUserSettings.addUser=Añadir Nuevo Usuario
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Roles
 adminUserSettings.role=Rol
 adminUserSettings.actions=Acciones
diff --git a/src/main/resources/messages_eu_ES.properties b/src/main/resources/messages_eu_ES.properties
index e67214c2..e24e3a7d 100644
--- a/src/main/resources/messages_eu_ES.properties
+++ b/src/main/resources/messages_eu_ES.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=User not authenticated.
 userNotFoundMessage=User not found.
 incorrectPasswordMessage=Current password is incorrect.
 usernameExistsMessage=New Username already exists.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Admin Erabiltzailearen Ezarpenen Kontrolak
 adminUserSettings.admin=Admin
 adminUserSettings.user=Erabiltzaile
 adminUserSettings.addUser=Erabiltzaile berria
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Rolak
 adminUserSettings.role=Rol
 adminUserSettings.actions=Ekintzak
diff --git a/src/main/resources/messages_fr_FR.properties b/src/main/resources/messages_fr_FR.properties
index 628792ae..809612d1 100644
--- a/src/main/resources/messages_fr_FR.properties
+++ b/src/main/resources/messages_fr_FR.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=Utilisateur non authentifié.
 userNotFoundMessage=Utilisateur non trouvé.
 incorrectPasswordMessage=Le mot de passe actuel est incorrect.
 usernameExistsMessage=Le nouveau nom d\u2019utilisateur existe déjà.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Administration des paramètres des utilisateurs
 adminUserSettings.admin=Administateur
 adminUserSettings.user=Utilisateur
 adminUserSettings.addUser=Ajouter un utilisateur
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Rôles
 adminUserSettings.role=Rôle
 adminUserSettings.actions=Actions
diff --git a/src/main/resources/messages_hi_IN.properties b/src/main/resources/messages_hi_IN.properties
index 8487dc81..ab08aa3c 100644
--- a/src/main/resources/messages_hi_IN.properties
+++ b/src/main/resources/messages_hi_IN.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=उपयोगकर्ता प्रमाणित
 userNotFoundMessage=उपयोगकर्ता नहीं मिला।
 incorrectPasswordMessage=वर्तमान पासवर्ड गलत है।
 usernameExistsMessage=नया उपयोगकर्ता नाम पहले से मौजूद है।
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=व्यवस्थापक उपयोगकर्
 adminUserSettings.admin=व्यवस्थापक
 adminUserSettings.user=उपयोगकर्ता
 adminUserSettings.addUser=नया उपयोगकर्ता जोड़ें
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=रोल्स
 adminUserSettings.role=रोल
 adminUserSettings.actions=क्रियाएँ
diff --git a/src/main/resources/messages_hu_HU.properties b/src/main/resources/messages_hu_HU.properties
index 97ed6630..c6ef560a 100644
--- a/src/main/resources/messages_hu_HU.properties
+++ b/src/main/resources/messages_hu_HU.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=Felhasználó nincs hitelesítve.
 userNotFoundMessage=A felhasználó nem található.
 incorrectPasswordMessage=A jelenlegi jelszó helytelen.
 usernameExistsMessage=Az új felhasználónév már létezik.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Adminisztrátori Felhasználói Vezérlési Beállítá
 adminUserSettings.admin=Adminisztrátor
 adminUserSettings.user=Felhasználó
 adminUserSettings.addUser=Új felhasználó hozzáadása
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Szerepek
 adminUserSettings.role=Szerep
 adminUserSettings.actions=Műveletek
diff --git a/src/main/resources/messages_id_ID.properties b/src/main/resources/messages_id_ID.properties
index 57f79f0c..96e77082 100644
--- a/src/main/resources/messages_id_ID.properties
+++ b/src/main/resources/messages_id_ID.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=Pengguna tidak ter-autentikasi.
 userNotFoundMessage=Pengguna tidak ditemukan.
 incorrectPasswordMessage=Kata sandi saat ini salah.
 usernameExistsMessage=Nama pengguna baru sudah ada.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Pengaturan Kontrol Admin
 adminUserSettings.admin=Admin
 adminUserSettings.user=Pengguna
 adminUserSettings.addUser=Tambahkan Pengguna Baru
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Peran
 adminUserSettings.role=Peran
 adminUserSettings.actions=Tindakan
diff --git a/src/main/resources/messages_it_IT.properties b/src/main/resources/messages_it_IT.properties
index bebce2bd..524c98cd 100644
--- a/src/main/resources/messages_it_IT.properties
+++ b/src/main/resources/messages_it_IT.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=Utente non autenticato.
 userNotFoundMessage=Utente non trovato.
 incorrectPasswordMessage=La password attuale non è corretta.
 usernameExistsMessage=Il nuovo nome utente esiste già.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Impossibile eliminare l'utente attualmente connesso.
 deleteUsernameExistsMessage=Il nome utente non esiste e non può essere eliminato.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Impostazioni di controllo utente amministratore
 adminUserSettings.admin=Amministratore
 adminUserSettings.user=Utente
 adminUserSettings.addUser=Aggiungi un nuovo Utente
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Ruoli
 adminUserSettings.role=Ruolo
 adminUserSettings.actions=Azioni
diff --git a/src/main/resources/messages_ja_JP.properties b/src/main/resources/messages_ja_JP.properties
index 09611c97..956f9562 100644
--- a/src/main/resources/messages_ja_JP.properties
+++ b/src/main/resources/messages_ja_JP.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=ユーザーが認証されていません。
 userNotFoundMessage=ユーザーが見つかりません。
 incorrectPasswordMessage=現在のパスワードが正しくありません。
 usernameExistsMessage=新しいユーザー名はすでに存在します。
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=管理者ユーザー制御設定
 adminUserSettings.admin=管理者
 adminUserSettings.user=ユーザー
 adminUserSettings.addUser=新しいユーザを追加
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=役割
 adminUserSettings.role=役割
 adminUserSettings.actions=アクション
diff --git a/src/main/resources/messages_ko_KR.properties b/src/main/resources/messages_ko_KR.properties
index 45d943e7..aa10e3c4 100644
--- a/src/main/resources/messages_ko_KR.properties
+++ b/src/main/resources/messages_ko_KR.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=User not authenticated.
 userNotFoundMessage=사용자를 찾을 수 없습니다.
 incorrectPasswordMessage=현재 비밀번호가 틀립니다.
 usernameExistsMessage=새 사용자명이 이미 존재합니다.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=사용자 관리
 adminUserSettings.admin=관리자
 adminUserSettings.user=사용자
 adminUserSettings.addUser=새 사용자 추가
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=역할
 adminUserSettings.role=역할
 adminUserSettings.actions=동작
diff --git a/src/main/resources/messages_nl_NL.properties b/src/main/resources/messages_nl_NL.properties
index dbc23d01..887a6813 100644
--- a/src/main/resources/messages_nl_NL.properties
+++ b/src/main/resources/messages_nl_NL.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=Gebruiker niet ingelogd.
 userNotFoundMessage=Gebruiker niet gevonden.
 incorrectPasswordMessage=Huidige wachtwoord is onjuist.
 usernameExistsMessage=Nieuwe gebruikersnaam bestaat al.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Beheer gebruikers
 adminUserSettings.admin=Beheerder
 adminUserSettings.user=Gebruiker
 adminUserSettings.addUser=Voeg nieuwe gebruiker toe
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Rollen
 adminUserSettings.role=Rol
 adminUserSettings.actions=Acties
diff --git a/src/main/resources/messages_pl_PL.properties b/src/main/resources/messages_pl_PL.properties
index 14d9c741..5ffccb4d 100644
--- a/src/main/resources/messages_pl_PL.properties
+++ b/src/main/resources/messages_pl_PL.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=User not authenticated.
 userNotFoundMessage=User not found.
 incorrectPasswordMessage=Current password is incorrect.
 usernameExistsMessage=New Username already exists.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Admin User Control Settings
 adminUserSettings.admin=Admin
 adminUserSettings.user=User
 adminUserSettings.addUser=Add New User
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Roles
 adminUserSettings.role=Role
 adminUserSettings.actions=Actions
diff --git a/src/main/resources/messages_pt_BR.properties b/src/main/resources/messages_pt_BR.properties
index 74cf8196..83171291 100644
--- a/src/main/resources/messages_pt_BR.properties
+++ b/src/main/resources/messages_pt_BR.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=User not authenticated.
 userNotFoundMessage=User not found.
 incorrectPasswordMessage=Current password is incorrect.
 usernameExistsMessage=New Username already exists.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Admin User Control Settings
 adminUserSettings.admin=Admin
 adminUserSettings.user=User
 adminUserSettings.addUser=Add New User
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Roles
 adminUserSettings.role=Role
 adminUserSettings.actions=Actions
diff --git a/src/main/resources/messages_pt_PT.properties b/src/main/resources/messages_pt_PT.properties
index 7d4da27f..06d33860 100644
--- a/src/main/resources/messages_pt_PT.properties
+++ b/src/main/resources/messages_pt_PT.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=Utilizador não autenticado.
 userNotFoundMessage=Utilizador inexistente.
 incorrectPasswordMessage=Senha incorreta.
 usernameExistsMessage=Esse utilizador já existe.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Admin User Control Settings
 adminUserSettings.admin=Admin
 adminUserSettings.user=User
 adminUserSettings.addUser=Add New User
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Roles
 adminUserSettings.role=Role
 adminUserSettings.actions=Actions
diff --git a/src/main/resources/messages_ro_RO.properties b/src/main/resources/messages_ro_RO.properties
index a28585db..66639555 100644
--- a/src/main/resources/messages_ro_RO.properties
+++ b/src/main/resources/messages_ro_RO.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=User not authenticated.
 userNotFoundMessage=User not found.
 incorrectPasswordMessage=Current password is incorrect.
 usernameExistsMessage=New Username already exists.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Admin User Control Settings
 adminUserSettings.admin=Admin
 adminUserSettings.user=User
 adminUserSettings.addUser=Add New User
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Roles
 adminUserSettings.role=Role
 adminUserSettings.actions=Actions
diff --git a/src/main/resources/messages_ru_RU.properties b/src/main/resources/messages_ru_RU.properties
index eeba0fea..5826ceef 100644
--- a/src/main/resources/messages_ru_RU.properties
+++ b/src/main/resources/messages_ru_RU.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=User not authenticated.
 userNotFoundMessage=User not found.
 incorrectPasswordMessage=Current password is incorrect.
 usernameExistsMessage=New Username already exists.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Admin User Control Settings
 adminUserSettings.admin=Admin
 adminUserSettings.user=User
 adminUserSettings.addUser=Add New User
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Roles
 adminUserSettings.role=Role
 adminUserSettings.actions=Actions
diff --git a/src/main/resources/messages_sr_LATN_RS.properties b/src/main/resources/messages_sr_LATN_RS.properties
index db33348b..0b195bcb 100644
--- a/src/main/resources/messages_sr_LATN_RS.properties
+++ b/src/main/resources/messages_sr_LATN_RS.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=Korisnik nije autentifikovan.
 userNotFoundMessage=Korisnik nije pronađen.
 incorrectPasswordMessage=Trenutna šifra je netačna.
 usernameExistsMessage=Novi korisnik već postoji
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Podešavanja kontrole korisnika za administratora
 adminUserSettings.admin=Administrator
 adminUserSettings.user=Korisnik
 adminUserSettings.addUser=Dodaj novog korisnika
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Uloge
 adminUserSettings.role=Uloga
 adminUserSettings.actions=Akcije
diff --git a/src/main/resources/messages_sv_SE.properties b/src/main/resources/messages_sv_SE.properties
index 9799dcf7..6adb3302 100644
--- a/src/main/resources/messages_sv_SE.properties
+++ b/src/main/resources/messages_sv_SE.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=User not authenticated.
 userNotFoundMessage=User not found.
 incorrectPasswordMessage=Current password is incorrect.
 usernameExistsMessage=New Username already exists.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Admin User Control Settings
 adminUserSettings.admin=Admin
 adminUserSettings.user=User
 adminUserSettings.addUser=Add New User
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Roles
 adminUserSettings.role=Role
 adminUserSettings.actions=Actions
diff --git a/src/main/resources/messages_tr_TR.properties b/src/main/resources/messages_tr_TR.properties
index 309c8286..0b50c054 100644
--- a/src/main/resources/messages_tr_TR.properties
+++ b/src/main/resources/messages_tr_TR.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=Kullanıcı doğrulanmadı.
 userNotFoundMessage=Kullanıcı bulunamadı.
 incorrectPasswordMessage=Mevcut şifre yanlış.
 usernameExistsMessage=Yeni Kullanıcı Adı zaten var.
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=Yönetici Kullanıcı Kontrol Ayarları
 adminUserSettings.admin=Yönetici
 adminUserSettings.user=Kullanıcı
 adminUserSettings.addUser=Yeni Kullanıcı Ekle
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=Roller
 adminUserSettings.role=Rol
 adminUserSettings.actions=Eylemler
diff --git a/src/main/resources/messages_zh_CN.properties b/src/main/resources/messages_zh_CN.properties
index 60ea640c..80a0d028 100644
--- a/src/main/resources/messages_zh_CN.properties
+++ b/src/main/resources/messages_zh_CN.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=用户未经过身份验证。
 userNotFoundMessage=未找到用户。
 incorrectPasswordMessage=当前密码不正确。
 usernameExistsMessage=新用户名已存在。
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=管理员用户控制设置
 adminUserSettings.admin=管理员
 adminUserSettings.user=用户
 adminUserSettings.addUser=添加新用户
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=角色
 adminUserSettings.role=角色
 adminUserSettings.actions=操作
diff --git a/src/main/resources/messages_zh_TW.properties b/src/main/resources/messages_zh_TW.properties
index 099b5ff5..cbf50e0e 100644
--- a/src/main/resources/messages_zh_TW.properties
+++ b/src/main/resources/messages_zh_TW.properties
@@ -53,6 +53,7 @@ notAuthenticatedMessage=使用者未認證。
 userNotFoundMessage=找不到使用者。
 incorrectPasswordMessage=目前密碼不正確。
 usernameExistsMessage=新使用者名稱已存在。
+invalidUsernameMessage=Invalid username, Username must only contain alphabet characters and numbers.
 deleteCurrentUserMessage=Cannot delete currently logged in user.
 deleteUsernameExistsMessage=The username does not exist and cannot be deleted.
 
@@ -145,6 +146,7 @@ adminUserSettings.header=管理使用者控制設定
 adminUserSettings.admin=管理員
 adminUserSettings.user=使用者
 adminUserSettings.addUser=新增使用者
+adminUserSettings.usernameInfo=Username must only contain letters and numbers, no spaces or special characters.
 adminUserSettings.roles=角色
 adminUserSettings.role=角色
 adminUserSettings.actions=操作
diff --git a/src/main/resources/templates/account.html b/src/main/resources/templates/account.html
index 4398891d..20501413 100644
--- a/src/main/resources/templates/account.html
+++ b/src/main/resources/templates/account.html
@@ -30,6 +30,9 @@
               <div th:if="${param.messageType[0] == 'usernameExists'}" class="alert alert-danger">
                 <span th:text="#{usernameExistsMessage}">Default message if not found</span>
               </div>
+              <div th:if="${param.messageType[0] == 'invalidUsername'}" class="alert alert-danger">
+                <span th:text="#{invalidUsernameMessage}">Default message if not found</span>
+              </div>
               </th:block>
               <!-- At the top of the user settings -->
               <h3 class="text-center"><span th:text="#{welcome} + ' ' + ${username}">User</span>!</h3>
diff --git a/src/main/resources/templates/addUsers.html b/src/main/resources/templates/addUsers.html
index 5e4f5f68..397b054a 100644
--- a/src/main/resources/templates/addUsers.html
+++ b/src/main/resources/templates/addUsers.html
@@ -42,13 +42,14 @@
               </table>
 
               <h2 th:text="#{adminUserSettings.addUser}">Add New User</h2>
-              <div th:if="${param.messageType != null and param.messageType.size() > 0 and param.messageType[0] == 'usernameExists'}" class="alert alert-danger">
-                <span th:text="#{usernameExistsMessage}">Default message if not found</span>
+              <div th:if="${param.messageType != null and param.messageType.size() > 0 and (param.messageType[0] == 'usernameExists' or param.messageType[0] == 'invalidUsername')}" class="alert alert-danger">
+                <span th:if="${param.messageType[0] == 'usernameExists'}" th:text="#{usernameExistsMessage}">Default message if not found</span>
+                <span th:if="${param.messageType[0] == 'invalidUsername'}" th:text="#{invalidUsernameMessage}">Default message if not found</span>
               </div>
               <form action="/api/v1/user/admin/saveUser" method="post">
                 <div class="mb-3">
                   <label for="username" th:text="#{username}">Username</label>
-                  <input type="text" class="form-control" name="username" required>
+                  <input type="text" class="form-control" name="username" pattern="[a-zA-Z0-9]+" th:title="#{adminUserSettings.usernameInfo}" required>
                 </div>
                 <div class="mb-3">
                   <label for="password" th:text="#{password}">Password</label>