Moved this to Malware Discussions > Home User Assistance for better attention.
Unfortunately antiviruses generally aren't very good at these fake anti-malware pests but there are tools available, free, that will kill it.
If necessary boot into Safe Mode with Networking by tapping F8 repeatedly while booting up if your desktop wont download or run anything.
Also you could try System Restore to before this happened, in which case, if successful, you should then temporarily disable System Restore to get rid of the infected restore point.
There's an excellent removal guide here: http://www.bleepingcomputer.com/virus-removal/remove-security-defender
+++Scroll down that page, do NOT click the first links you see as they are all advertising which helps pay for that web site.
If you go the restore route don't forget to update everything afterwards.
Message was edited by: Ex_Brit on 28/02/11 9:50:15 EST AM
Is your machine infected? If yes please share what steps have been performed if any and what is the current state.
if the machine is malware free glad to learn that.
As a first step you could boot the machine to safe mode with networking and scan the machine with the existing AV product .. Many of these infection are not active in safemode and hence could help detection and removal