Microsoft Security Essentials
Avast!
AVG
Malwarebytes Anti-Malware(Download this along the anti-virus you choose)
I personally use MSE/MBAM, but it's up to you what to choose.
And just to confuse people after putting a random picture in the Instant and Moment thread, I'm making a text post with no pictures in this one!
I AM SUCH AN ANARCHIST
...
Alright, fine, here's TF2 birds.