The Trojan takes advantage of one controversial feature of Microsoft's Windows Genuine Advantage anti-piracy mechanism: revalidation. To receive most downloads, including Internet Explorer or anything from the Windows Update Web site, end users must validate that their computers are, in Microsoft parlance, "genuine." But one validation isn't enough. Microsoft has Windows clients periodically revalidate.

The process is designed to catch new pirated versions as Microsoft continually updates its piracy database.

Microsoft-Watch