what is it?
windll.exe is a file associated with the worm W32.Beagle.AQ@mm
this worm is a variant of W32.Beagle.AO@mm, which is a mass-mailing worm that uses its own SMTP engine to spread

what does it do?
Among other bad things, this worm Copies itself as the following files:

• %System%windll.exe. (A copy of the worm)
• %System%windll.exeopen (A copy of the worm)
• %System%windll.exeopenopen (A copy of the worm

Removal
Read more about this nasty bug and how to remove it @symantec