There is apparently an email campaign going on to infect your computer with a new virus.
The legitimate looking email seems to come from Microsoft and invites the reader to go to the Microsoft update site to get access to the latest security updates. The site seems to be a good copy of Microsoft's Web site and lures the visitor into downloading a Windows security patch.
But should unsuspecting users download the bogus patches, they will infect their computers with the Troj/DSNX-05 Trojan horse, according to Sophos. That, in turn, will let the attackers remotely take control of the infected PC. ZDNet
Microsoft is quick to point out that they never contact users by email for security updates.