Download and run Malwarebytes, if malware, etc., appears (listed in red) delete. If you like AVG go to a box store and buy the full version the free version doesn't give you what you need to preclude some issues, including the one you have described.
I recently have been hit with a virus that is sending out a link to sites to all my contacts on my Contact list in windows live. Im running a firewall and i also run the avg Free 2010 version and it still does not seem to find it. I have changed my password 4 times and in each case it still manages to find it and I'm frustrated and clueless how else to attack this situation. This computer is a athalon 2.6 gig quad core, and im running windows xp. Any info would be welcome , thank you