Everyone on the internet needs an antivirus program. You should have one before you even log on for the first time. I recommend getting the very best: http://www.nod32.com/home/home.htm

But if paying for an antivirus is not in your budget, I recommend AntiVir Personal Edition.
http://www.majorgeeks.com/download955.html 

One piece of security software I recommend is, Sygate’s personal firewall. While software firewalls aren’t all that good against stopping hackers compared to hardware based firewalls (if you have a router then you have one), they do give you the easy ability to prevent programs on your computer from accessing your internet connection.
http://www.sygate.com/ 

I recommend that everybody get some anti-spyware software. This will remove some of the programs that advertise to you on your computer, as well as some of the more nasty unwanted softwares such as some viruses.
http://www.lavasoftusa.com/ Adaware, also downloadable from download.com

Another anti-spyware tool I use in conjunction with Adaware is Spybot Search & Destroy. It will catch some things Adaware won’t, but it is geared towards the more advanced users.
http://www.safer-networking.org/ 

Yet another anti-spyware tool that I consider a must have is Spyware Blaster. The great thing about it is it uses no system resources, it simply tells your browser some places where it shouldn’t go
http://www.javacoolsoftware.com/ 

Click to save the rainforest.
http://rainforest.care2.com/ 

Any questions? http://groups.yahoo.com/group/computer_builder_hardware/