Group of hackers called "Anonymous" are out taking over people computers to DOS various sites. So PLEASE be sure to scan what you download, and your entire computer full scan and all.
Anonymous is a group who is to be taken very serious, and if I'm paranoid you should be to. They've hacked into government severs, and more before so please do take this serious.
Here's a list of free anti-virus and firewall programs you can use.
RemoveIt Pro v4 SE
+I personally recommend these, also keep them updated. They all work on XP, Vista, Windows 7, and can be installed side by side w/o any issues.
Again this is a warning to help protect you.