The best known free anti-virus program is AGV: http://free.avg.com/

But I would recommend that you go with a paid solution such as either McAfee or Norton.  Paying for it will give you regular updates.  Without those updates, you are not protected from the latest threats.  Being protected from the latest threats is most important since viruses and spyware tend to run their course and “die” off after some period of time.

I use Norton. http://www.symantec.com/norton/antivirus  ($39)

If you have Comcast internet, you can get McAfee for free: http://www.comcast.net/Security/SecSuiteSSO/?cid=NET_33_10

In addition to Anti-Virus software, you need to have Anti-Spyware software.  I use Spyware Detector http://spywaredetector.com/  ($29)

My computer gets 2-4 Spyware issues per day (usually pretty harmless cookies, versus problematic programs), but I have not had a virus in more than a year.  I run a full spyware scan every night and a virus scan once per week.

The best protection against viruses and spyware is to run Windows as a guest account instead of as administrator and to not open any email attachments that fit these criteria:

1)       never open an attachment that has a .vbs, .bat, .com, .exe extension; ever

2)       never open an attachment that was sent from some one you do not know no matter what type of file it is

3)       never open an attachment unless the sender mentions it in the email

Logging into Windows as a guest is a real pain, but it locks Windows down tight so that it is extremely unlikely that anything will be able to be installed.  I have my kids run as guest.

The process for setting up a guest account is somewhat involved.  It would be best if you took your computer to one of these three places:

1)       Feather Computers on Lawrenceville Highway across from Shamrock Plaza, behind Krystal’s

2)       Onyx Consulting in Decatur behind McDonald’s

3)       Geek Squad at Best Buy

They could also install the software you need and make sure it is configured correctly.