So on Wednesday,April 24, 2010, McAfee released a virus definition update which basically messed up all of the Windows XP Service Pack 3 computers using their services (with "Scan Processes on Enable" option on).

This buggy virus definition update basically flagged the svchost.exe process, and quarantined it.

However, the computers with the "Scan Processes on Enable" option on, were then stuck in an infinite loop, where the virus scanner killed the process, and the computer rebooted, only to have the scanner auto kill the process on startup again.

This messed up many companies using their services, such as a large part of Intel, Snohomish County, etc.

McAfee released some instructions for the affected customers here: https://kc.mcafee.com/corporate/index?page=content&id=KB68780

Sources:

• http://www.networkworld.com/news/2010/042210-few-answers-after-mcafee-antivirus.html
• "Coles closes stores due to McAfee bug" at ZDNet Australia.
• How to fix your McAfee-crippled computer
• McAfee to compensate home users for bad update

Related articles: the Top Computer Security Software of 2010 and the Top Computer Security Software of March 2010.