I have installed Kaspersky in infected pc. It just delete important system files and makes the system handicapped. It gives only one option to user after a restart do a clean install of windows. I think this is the way it clean virus in a pre-infected pc, if it clean then it takes ages to clean a single file and several restart. I am talking about both Kaspersky Internet Security 2011 and Kaspersky Internet Security 2012(In which they say they have improved alot) ;D ;D
But if its installed on a clean pc then it never allow a single virus to enter.