The googleupdate.a3x file belongs to a worm called Verecno.
Your computer was unfortunately infected by this worm. Your antivirus has already removed it but some of its files are still present, that's why you see this error each time you start Windows.
To get rid of this error, open the registry editor by pressing the Windows + R keys at the same time on your keyboard. Type regedit, then press Enter.
- Navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
- Delete the entries autoit3.exe, windowsupdate.lnk and googleupdate.a3x.
- Do the same in HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
Next, run a full scan of your computer using your antivirus or Microsoft Security Essential / Windows Defender to make sure that Verecno is completely removed from your system.