When I first got my computer 2 years ago, I immediately bought
McAfee's anti-virus software.  It worked great, but when it was time
to renew it after a year and I was tight on money, I tried AVG's free
anti-virus program.  I was skeptical at first because it was free, but
it's been a year since I've had it, and it's actually really good.  It
constantly updates itself, and it caught malware that was trying to
infect my computer the other day pretty quick.  AVG also has programs
that you do have to buy that have more features, but the free version
that I have covers basic stuff like anti-virus, anti-spyware, and a
computer scanner that checks computer files for bad stuff.  It can
also do identity protection, but I think you have to pay for that.
Anyway, for a free program, I think that AVG is a great deal.  Their
web site is www.avg.com.  You can also find more information on what
stuff like viruses, malware, and spyware do and also program review
sites on my blog at http://computersoftwarereviews-jnewvista.blogspot.com/.