What I can download to protect my computer for free?

MalwareBytes.

AVG

Spybot Search and Destroy

Grisoft Zone Alarm (it gives lots of alerts until it “learns” your habits, but nothing would get through without you knowing.)

Trendwest Ad-Aware.

Avira
Spybot S&D

I have had good luck with Microsoft Security Essentials.

I have AVG and it works really well. It will probobly work on new ones best, too.

There’s a lot of offline protection, you should read some reviews and see which one best fits you.

For online protection, I suggest Norton Safeweb Lite.

I like Microsoft Security, too.

Also: [mod says] This is our Question of the Day!

Threatfire

Keep in mind that some good security practices are better than anti-virus programs.

-Create a separate user account for daily use.
-Do not use IE. Firefox and Chrome are better.
-Don’t click on e-mail attachments unless you expect them. My mom sent me the Paris Hilton sex tape and it was a exe file. But she didn’t actually send it. Something sent it to all her contacts. I did make a hundred bucks cleaning all that up for her.
-Do not install random shit from the internet. There are lots of scam sites with virus laden versions of legit software. I have searched for stuff on google and had the bad version rank higher than the real version.