www.download.com
First off i would suggest getting two programs. Both from that link. First do a search for Ad-Aware. Make sure you get the free one! Its definatly by far one of the best programs out there for spyware detection and removal. This program basically finds/removes any malicious software. I would recommend updating and running it ATLEAST once per week. I usually run it about every other day. You will be shocked at its first results. This program usually fixes problems of computer slow-down, or time-out issues, due to the programs running in the background. You may not know it but they are there! How do these programs get installed you ask? Just by having an internet connection. Obviouslly the worst places to pick them up is porn sites and warez game sites. But just casual veiwing of the internet can catch spy-ware. They can even send it directly to your computer if you have an open internet connection such as cable, DSL, LAN, etc. Thats where the second program comes into play.
www.download.com
Search for zonealarm. You want the free one again! This is a firewall. It basically protects intrusions in/out of your PC. Its a great program but tends to give those not-so-computer savy people a lil headache. Whenever there is an intrusion it pops up a message that tells who/what program is trying to gain internet access. If this message comes up for no reason when you arent using programs or accessing the internet and you do not recognize the vendor i would always block them. But vice-versa i would always allow it. Or if its that much of a pain just post me a message i would be more than happy to consult you on it.
I could go into detail on both and write up a few pages but ill leave you with this for now. I use both of these programs on my personal PC and have not had problems since. But then im avid about keeping my PC clean. These programs do not take place of anti-virus. Even though i never have to use my anti-virus program because of these i strongly suggest you keep the one you currently are using or go buy one. And again post any questions if you want feedback. I enjoy what i do, so feel free!