Received three laptops today with the same virus...  fake Anti-Virus that looks like windows security center telling you that you're infected, when you click to remove the viruses it asks for your credit card saying your Anti-Virus has expired... DON'T GIVE YOUR CREDIT CARD!  Not only will it "pretend" to remove the viruses but your PC will stay infected and worse of all your credit card details will end up in Nigeria or somewhere bad!! 5 Basic precautions will prevent this:

[1] Only download from legitimate sites i.e. microsoft, cnet, 
[2] Dont use Torrents, P2P sharing or similar! Will always end in tears! 
[3] Ensure your Anti-Virus software such as Nortons, McAfee, AVG, Microsoft Security Essentials (my recommendation) etc are updated and NOT EXPIRED!!!!  If your paid AntiVirus has expired, download Microsoft Security Essentials from the Microsoft website only (make sure you remove your old Anti-virus software first!). 
[4] Don't open email attachments! Even ones that could be from your friends could be a virus. Get your friends to share pictures on Facebook / photobucket etc rather than send in an email, NEVER open .exe or .SCR files from an email 
[5] Use common sense!

If you are not sure ask me and I will try to help.