Until someone from Corporate answers you I'll offer a few suggestions.
First try to invoke System Restore to go back to before it happened. This can be started in regular or Safe Mode.
Or, try running Rootkit Remover and Stinger, both listed in the last link in my signature below.
If it keeps reappearing it could be simply reactivating from garbage files so do a Disk Cleanup and make sure the Recycle Bin and Temporary Files are selected in the options.
How to access Disk Cleanup in XP: http://www.theeldergeek.com/disk_cleanup_utility.htm
How to Access Disk Cleanup in Vista: http://www.vistax64.com/tutorials/76073-disk-cleanup.html
How to access Disk Cleanup in Windows 7: http://www.sevenforums.com/tutorials/818-disk-cleanup-open-use.html