The downside of the Internet:
Pop-up ads, spyware, trojans, and a proliferation of viruses

I regularly encounter computers that operate slowly and produce lewd pop-up windows. In these situations I often uncover spyware and trojans, data gathering programs that run on your computer for the benefit of someone else. Spyware actually monitors your Internet activity and reports it to advertisers. Trojans are installed by hackers who can then use your computer as a launching pad to attack or break into other computers. Thousands of computers routinely transmit advertisements and spam without their owners even knowing about it.

What to do?
Removing spyware can be done manually but there are inexpensive tools to do the job thoroughly. I usually run a free version of Adaware a couple times a week. It removes tracking cookies and other malicious code that track your Internet activity and report it to advertisers. I use it in conjunction with Spybot Search and Destroy. Finally, you can also use a program, such as Trackless, to thoroughly erase your internet history and temporary files and thereby eliminate potentially malicious software before it infects your PC.

Another very useful thing to do is to install a pop-up ad blocker. There are dozens of these on the market but I use the one included in Symantec's Norton Personal Firewall. When configured properly, this software will eliminate all advertisements on your webpages and keep pop-ups from finding their way into your life.

While both of these problems are obnoxious, they pale in comparison with trojans and viruses, which can literally destroy your computer or at least make it run very slowly. Once again there are many commercially available products but I tend to use Symantec's Personal Firewall and and anti-virus programs because they are easy to install and maintain. However, if you are fairly computer literate, Zone Alarm makes an excellent firewall. And Grisoft makes one of the best free anti-virus program out right now.

To check on your current system, Symantec provides a free security check that searches for trojans. Gibson Research has a several free utilities, including one that evaluates your computer for potential exposure to hackers and another that disables some security flaws inherent in Windows XP.