get a lot of e-mail from readers asking what criminal hackers can and can't do to the average home PC. In most cases, I'd say home systems are fairly safe, if only because each computer is a needle in a giant haystack called the Internet. While the profile of the criminal hacker (for whom I prefer the term "cracker") suggests a young male who is both patient and obsessive, most of these individuals would rather stalk the big fish--university, government, and commercial systems--than your computer.

I don't mean to say home PCs aren't targets. They are. Crackers keep track of IP addresses assigned by Internet service providers to dial-up, DSL, and cable-modem users. Some regularly scan those addresses, looking for PCs that are connected to the Net and that have known security vulnerabilities.

These lists of vulnerable computers are often traded or sold over the Internet, and help virus writers plant their viruses quickly. That's why it's important to use firewall software and keep all your applications updated with the latest patches.

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