Crispy said:

Microsoft security solutions have helped clean over 13 million computers worldwide infected with rogue antivirus software in 2009. However, according to volume eight of the Microsoft Security Intelligence Report (SIRv8), fake antivirus is a growing problem, with the number of compromised computers having grown in the second half of 2009 compared to the first half of the past year. In SIRv8, Microsoft reveals that its security products detected and cleaned rogue security software, as well as malware variations of fake AV, from no less than 7.8 million computers in the second half of the past year.

Microsoft security products identified 2.5 million more face AV infections in 2H 2009 over the first half of the previous year. Between January and June 2009, only 5.3 million instances of rogue security software were cleaned from compromised computers worldwide. The Redmond company concludes that attackers are choosing to focus increasingly on spreading rogue AV, precisely because they can monetize the malicious code better than other malware.

Full read: Over 13 Million PCs Infected with Fake Antivirus Cleaned in 2009 - By Microsoft security solutions - Softpedia

Thats why i posted a topic and a solution about this. Its becoming so common now.