With this Tweak you can change the message shown on the logon box.

To change this, follow the next steps:

1. Open the Registry Editor click on the Start button on your taskbar, then click on Run and type "regedit" and click on OK to start the regedit utility.
    
2. Expand HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon (see picture 1).
   
   

   Picture 1

3. Modify the value named "LegalNoticeCaption" to represent the caption on the dialog box (e.g. 'WARNING!'). If this value doesn't already exist create it. Modify the value named "LegalNoticeText" to represent the body of the dialog box (e.g. 'Do Not Attempt to Logon to this system unless you are an authorized user!')
   
   
4. The modifications you made will be in effect after you reboot your PC.