What's the best free virus scanner?

avast, the very best one

as for the slow pc, maybe you have too much installed software occupying your ram,

Not being there it's hard to guess. I am assuming you are defragmenting your drive on steady bases? You can download ccleanner and get rid of all the junk that will accumulate on your computer over time. You can also download Malwarebytes to make sure your computer is clean. I use Comodo Internet Security but it can be demanding. If you want something easy Avast or Microsoft Security Essentials would be way to go. Even Panda Cloud is not a bad choice. If you want to pay Norton or Kaspersky are the best right now. I really hope you have some security right now.

Avast! Free Antivirus

http://www.avast.com/

Avira AntiVir Personal Edition

http://www.avira.com/

Microsoft Security Essentials (MSE)

http://www.microsoft.com/security/pc-security/mse....

More free antivirus software:

http://deletemalware.blogspot.com/2011/08/free-ant...

use avast for anti-virus and malwarebytes and get ccleaner to get all the junk off your computer run one at a time all are free get all at filehippo.com or cnet.com hope this helps

Microsoft security essentials is for windows, it is free and fast.