Susan sent an e-mail asking about false positives. She wants to know how people can be certain that warnings are not true. She worries that she could end up with threats on her computer.

I understand your concern, Susan. But the people who work this way are mostly crooks.

If you don't believe that, you could try this test. These are almost always pop-ups. They show up when you surf. You could let them run their "scan." They'll tell you that you have numerous pieces of malware. And they'll offer to clean your computer. All you have to pay is $30 or $40.

Let's say you follow through. You buy their product and run it. That should clean up the computer, right? Well, if you see that pop-up again, the same things will happen.

Believe me, I get messages regularly from people who have been gypped. Often, they end up with pop-ups on their computers. Doing business with these people is dangerous.

The truth is, if you use common sense, you'll be OK. Delete spam right away; don't read it. People who play around with that stuff get socked, sooner or later. Keep your antivirus program up to date. Same goes for your anti-spyware programs.

Use a firewall. I like the one from ZoneAlarm. It's much more capable than the one in Windows. You could also try Outpost Firewall.