1. Make sure that you have all the updates for your computer by going to www.windowsupdate.com
and that you have updates for your antivirus programs such as AVG and adaware.
2. Download Spybot search and destroy. This will get rid of some of the spyware that adaware doesn't detect. This will also need to updated once you download this.
3. Download Spyware blaster. This will prevent spyware and adware from even getting in your computer in the first place. This program is great. Since I've downloaded it I haven't had any troubles and spybot and adaware haven't detected anything.
all the programs I just said are available free for download and you can get all of them at www.majorgeeks.com
and just do a search there on the right hand side. Run these things like every week or so.
As for whether or not those programs off of ebay work or not. I would not buy a program like that off of ebay. For one, most of them contain spyware and viruses themselves, so they are no good.
By the way, just because a program is free doesn't mean it isn't good. All these programs are free and they are excellent. They all catch things that my Norton Antivirus 2004 doesn't. Don't doubt freeware
As for buying other Antivirus software such as AVG. Don't because if two antivirus programs are running at the same time it can be deadly. This doesn't apply for spyware blaster though. You can run spyware blaster and another antivirus client such as AVG at the same time and it won't do anything.
I hope this helps a little bit.