1. Go to Run and type "regedit"
(No quotations)

2. Press the plus by "HKEY_LOCAL_MACHINE"

3. Then the plus by "SOFTWARE"

4. Then "Microsoft"

5. And then go to "WindowsNT"

6. Go to "CurrentVersion"

7. Then "Winlogon"

8. Then "SpecialAccounts"

9. And finally just click on "UserList"
don't press the plus

10. Right click and create a "DWORD" value

11. Put the value name as the hidden user account name

12. And set the "Value Data" to 0

13. Exit the window then reboot.

NOTE: To make this less suspicious use the windows welcome screen instead of the plain text one. The welcome screen shows all user accounts except the hidden one. Now to login from the welcome screen, hold CTRL+ALT and double tap DELETE. This will show the plain text version of the welcome screen that does not display user accounts. Simply put in the hidden user account's user name and password and you're in.

TIP: To hide all users starting with a phrase, for example, 'wtv_', create a DWORD called 'wtv_' and set it to 65535.