I have no antivirus on my laptop and rarely ever use it – knock on wood. (I am mindful, and keep backups. ) FYI: “Window Antivirus 2009” IS A Virus despite its name. I had to teach my wife to stop clicking on it to ‘Scan your infected system now’ on her computer. I hear so many virus stories, if you don’t have Antivirus installed - then go get one, and there are free ones that are just as good as the paid versions. (If you have a MAC/linux you are smiling right now.)
The best free one – that’s adware free is AVG Antivirus software (http://free.avg.com). Send it to all your friends (except for radical liberals) that are unprotected. Its free antivirus without the extra baggage. I have installed it on dozens of computers without issue. Also I hear as an alternative: Avira Antivirus is good, but I’d stick w/ AVG.
More tips: Windows Defender (http://www.microsoft.com/windows/products/winfamily/defender/) - Windows XP users install this. It comes installed with Windows Vista. It's from Microsoft and stops spam, pop-ups, and other stuff.
Always be mindful when installing ANYTHING that you just Googled.