I did a little research and I'm assuming you have XP. Logonui.exe is your OS Logon/Welcome screen. By default it resides in your "C:\Wondows\System32" folder. According to search results, a Virus version gets placed in your "C:\Windows" or "C:\Program Files" directory and the registry points to that version. Recommend good AV/Spyware/Malwar software scan.