Index: xwiki-core/src/main/java/com/xpn/xwiki/user/impl/xwiki/XWikiAuthServiceImpl.java
===================================================================
--- xwiki-core/src/main/java/com/xpn/xwiki/user/impl/xwiki/XWikiAuthServiceImpl.java	(revision 18352)
+++ xwiki-core/src/main/java/com/xpn/xwiki/user/impl/xwiki/XWikiAuthServiceImpl.java	(working copy)
@@ -381,36 +381,47 @@
         // This is needed for virtual mode to work
         if (context != null) {
             String susername = cannonicalUsername;
+            String virtualXwikiName = null;
             int i = cannonicalUsername.indexOf(".");
             int j = cannonicalUsername.indexOf(":");
 
             if (i != -1) {
                 susername = cannonicalUsername.substring(i + 1);
-            } else if (j != -1) {
+            } else if (j > 0) {
                 // The username could be in the format xwiki:Username, so strip the wiki prefix.
+                // read the Virtual Wiki Database Name
                 susername = cannonicalUsername.substring(j + 1);
+                virtualXwikiName = cannonicalUsername.substring(0, j);
             }
 
-            // First we check in the local database
+            String db = context.getDatabase();
+
             try {
-                String user = findUser(susername, context);
-                if (user != null) {
-                    if (checkPassword(user, password, context)) {
-                        return new SimplePrincipal(user);
+
+                // Set the context database to the virtual wiki database name.
+                if (virtualXwikiName != null)
+                    context.setDatabase(virtualXwikiName);
+
+                // Check in the local database or database with virtual xwiki name.
+                try {
+                    String user = findUser(susername, context);
+                    if (user != null) {
+                        if (checkPassword(user, password, context)) {
+                            return new SimplePrincipal(virtualXwikiName != null ? context.getDatabase() + ":" + user
+                                : user);
+                        } else {
+                            context.put("message", "wrongpassword");
+                        }
                     } else {
-                        context.put("message", "wrongpassword");
+                        context.put("message", "wronguser");
                     }
-                } else {
-                    context.put("message", "wronguser");
+                } catch (Exception e) {
+                    // continue
                 }
-            } catch (Exception e) {
-                // continue
-            }
 
-            if (!context.isMainWiki()) {
-                // Then we check in the main database
-                String db = context.getDatabase();
-                try {
+                if (!context.isMainWiki()) {
+                    // Then we check in the main database
+
                     context.setDatabase(context.getMainXWiki());
                     try {
                         String user = findUser(susername, context);
@@ -429,13 +440,15 @@
                         context.put("message", "loginfailed");
                         return null;
                     }
-                } finally {
-                    context.setDatabase(db);
+
+                } else {
+                    // error message was already set
+                    return null;
                 }
-            } else {
-                // error message was already set
-                return null;
+            } finally {
+                context.setDatabase(db);
             }
+
         } else {
             context.put("message", "loginfailed");
             return null;
Index: xwiki-core/src/test/java/com/xpn/xwiki/user/impl/xwiki/XWikiAuthServiceImplTest.java
===================================================================
--- xwiki-core/src/test/java/com/xpn/xwiki/user/impl/xwiki/XWikiAuthServiceImplTest.java	(revision 18352)
+++ xwiki-core/src/test/java/com/xpn/xwiki/user/impl/xwiki/XWikiAuthServiceImplTest.java	(working copy)
@@ -123,4 +123,58 @@
         assertNotNull(principal);
         assertEquals("XWiki.SomeUser", principal.getName());
     }
+
+    /**
+     * Test that user is authenticated with a global account when a local one with the same name exists.
+     */
+
+    public void testLogintoVirtualXwikiWithWikiPrefixUsername() throws Exception
+    {
+
+        // Setup a simple user profile documents
+        XWikiDocument userDocLocal = new XWikiDocument("local", "XWiki", "Admin");
+        XWikiDocument userDocVirtual = new XWikiDocument("xwiki", "XWiki", "Admin");
+
+        // Make a simple XWiki.XWikiUsers class that will contain a default password field
+        BaseClass userClass = new BaseClass();
+        userClass.addPasswordField("password", "Password", 20);
+        userClass.setClassName("XWiki.XWikiUsers");
+
+        // Mock the XWikiUsers object, since a real objects requires more mocking on the XWiki object
+        Mock mockUserObj = mock(BaseObject.class, new Class[] {}, new Object[] {});
+        mockUserObj.stubs().method("setWiki");
+        mockUserObj.stubs().method("setName");
+        mockUserObj.stubs().method("setNumber");
+        mockUserObj.stubs().method("getStringValue").with(eq("password")).will(returnValue("admin"));
+        userDocLocal.addObject("XWiki.XWikiUsers", (BaseObject) mockUserObj.proxy());
+
+        // Prepare the XWiki mock for local
+        this.mockXWiki.stubs().method("getDocument").with(eq("XWiki.Admin"), eq(this.getContext())).will(
+            returnValue(userDocLocal));
+        this.mockXWiki.stubs().method("getClass").with(eq("XWiki.XWikiUsers"), eq(this.getContext())).will(
+            returnValue(userClass));
+        this.mockXWiki.stubs().method("exists").will(returnValue(true));
+        this.mockXWiki.stubs().method("isVirtualMode").will(returnValue(false));
+
+        // Run the test: Using Xwiki.Admin should correctly authenticate the Admin user
+        Principal principalLocal = this.authService.authenticate("XWiki.Admin", "admin", this.getContext());
+        assertNotNull(principalLocal);
+        assertEquals("XWiki.Admin", principalLocal.getName());
+
+        // Set the database name to local.
+        this.getContext().setDatabase("local");
+
+        // Prepare the XWiki mock for virtual
+        this.mockXWiki.stubs().method("getDocument").with(eq("XWiki.Admin"), eq(this.getContext())).will(
+            returnValue(userDocVirtual));
+        this.mockXWiki.stubs().method("isVirtualMode").will(returnValue(true));
+        userDocVirtual.addObject("XWiki.XWikiUsers", (BaseObject) mockUserObj.proxy());
+
+        // Finally run the test: Using xwiki:Xwiki.Admin should correctly authenticate the Admin user
+        Principal principalVirtual = this.authService.authenticate("xwiki:XWiki.Admin", "admin", this.getContext());
+        assertNotNull(principalVirtual);
+        assertEquals("XWiki.Admin", principalVirtual.getName());
+
+    }
+
 }