What I have used Before Is Zonealarm Free firewall... WHich worked great never had any virus problems. Then I go vista and Only used vista firewall untill i just spent money for norton internet security for 70 dollars. Also Spybot Seach and Destroy will help.(Free) Spyware blaster which adds bad sites to a resticted list. AVG free is good virus protection. Used it forever. The last thing that I can think of that would be free is Mcafee Security Suit Free from AOL. I didnt like it because It took up allot of my pc resources but.. I only had 752 mb of ram and a old ibm thinkpad so. I think that You can still get this free offer at this link. You should only have one anivirus software.. Like AVG and One firewall. If you get Mcafee free you will not need avg. Because Mcafee has a virus protection incuded. Sbybot search and Destroy is okay to have allong side of a security suit. So is spyware blaster.
So Here are your chices for best security:Mcafee Free from aol, With spybotsearch and Destroy, and Spyware Blaster.
Or you can have Zonealarm free with avg Free and Spybot, and Spyware Blaster.
The last choice is to buy a good security suit and Norton is supposed to be the best. 50 dollars at wallmart.(Igot mine at circut city and It is cheaper at wallmart.)
The last thing that Is very important is to not use p2p. Bittorent Limewire. Illegal, Yet fun and free and its like shopping for free movies and music but it is asking for viruses. I dont listen to this ruel but I am trying my best to stop.
One other alternative just for scaning is Panda Active scan. Free online scan for viruses it will not remove but You will atlead know and Find a good tech support forum where they can help you. Dont remove any viruses manually. A good free tech support forum is Techsupportforums.com They help me allot I use them all the time.
Here is the link to mcafee-
WWW LinkAVG Free-http://daol.aol.com/security/virusscan-plus
Spybot s&d-http://www.safer-networking.org/index2.html
Just check out this artical for more information on computer security-http://www.techsupportforum.com/security-center/general-computer-security/115548-pc-safety-security-what-do-i-need.html