Spyware is not noticeable until, say, you start losing your Internet connection. I had installed a freeware program which unbeknownst to me, also installed a little spyware program called WebHancer. Since WebHancer routes all your Internet traffic through itself so it can happily report to the home office where you've been surfing, it a) will slow down your Internet, b) may not let other users on your machine (if using NT/2000) on the Internet at all. Very annoying.

What's really annoying is that often you're not told that they're installing these programs and certainly won't give you the option to not install them. Sometimes you won't even find an un-install option in Add/Remove Programs. And when you're trying to delete the files they're most likely in use and therefore won't go away. Removing these programs is a multi-step process. The best program I have found to rid yourself of this vermin is AdAware by our German friends from Lavasoft. It will also get rid of other annoyances such as Gator, Bonzi Buddy, and more.

For great info on spyware, check out voiceoftherepublic.com and www.cexx.org.