Ready for this gem? I had an e-mail from a reader recently with a troubleshooting question. He told me that no programs were running on his stand-alone PC, yet documents would pop out of his printer. Occasionally the CD-ROM tray would open unexpectedly. Much as I'd like to blame it on a bug in Windows, it turns out the guy had a Trojan horse, and some hacker was probably laughing their head off.

You may not be familiar with how a Trojan horse works. Unlike a virus that deletes files or JavaScript that sends e-mail to everyone in your address book, think of a Trojan horse as a remote-control tool. It quietly sits in the background, waiting for you to go online, and for the hacker to load it. You can infect your system with a Trojan horse by clicking (and thereby executing) an e-mail attachment.

There are two good ways to block and eliminate Trojan horses: firewalls and Trojan horse scanners (more about them in a sec).

Is Your PC Wearing Protection?

For a solid backgrounder, read our "Net Threats" special report. We tackled everything, including Trojan horses, Net surveillance, electronic-commerce rip-offs, financial swindles, hackers, and the tools you need to defend yourself against such hazards.

If you do nothing else, at least read what a Trojan horse can do in "Technology Attacks: Trojan Horses and Other E-Flimflams."

Then visit About.com's Trojan horses page.

In "Bugs and Fixes: Entertainment--With Hack Included," Stuart J. Johnston gives you the straight skinny on keeping snoops away from your data. You'll also find valuable links for Internet Explorer patches.

Now that you're interested, it's time for you to learn the difference between Back Orifice and DoS attacks. It's all at Andrew Brandt's "Hacker Speak."

Fire Up That Wall

Even if you go online only occasionally, you still need protection, and your best defense against hackers and Trojan horses is a firewall. The one I use is ZoneAlarm from ZoneLabs. It's a freebie, and Cameron Crouch talks about it in "ZoneAlarm Introduces a Friendlier Firewall."

Then shift to Robert L. Hummel's tutorial "How It Works: Personal Firewalls."

With a little firewall knowledge under your belt, you're ready for Stan Miastkowski (no, I can't pronounce it either--I send him e-mail instead) and his comprehensive "Fortress PC." The guy must have spent months researching and testing firewalls (and probably kvetching to his editor the whole time). It's a terrific resource for you to read.

Hardwired Firewalls

I'll bet some of you have three or four PCs networked, all sharing the same high-speed connection. Do yourself a favor and grab a hardware firewall. I'm playing with SOHOware's BroadGuard NBG800, a router that connects my wife's PC, my system, and two test machines. The four-port, 10/100-mbps device has a built-in firewall, with support for virtual private networking and Network Address Translation.

If you have obnoxious teenagers on the network, you can see where they're browsing and restrict their surfing activities. If you leave the office and a hacker tries, say, a denial-of-service attack--a technique that slows down your Web site's performance by rapid, repeated requests--SOHOware's firewall sends you an e-mail. It discounts for about $160.

Dig this: Feeling anxious that someone might hack into your PC? Take a break and check out this amazing series of captured radar images of migrating birds. They're from Intellicast's NEXRAD radar, and the site's author combined them into animated GIFs.

If you already have a firewall in place, take a second to see how well it's working. Read "Security Crusader Punches Holes in Firewalls." You'll see how security guru Steve Gibson's free tool easily tricked firewalls from McAfee.com, Symantec, Sygate, and others.

Then grab a copy of Gibson's LeakTest.

Even if you have a firewall in place, Michael S. Lasky's "Protect Your Data: The Ten Commandments of Internet Privacy" is worth a quick once-over.

And see Dennis O'Reilly's short and sweet "To Tell or Not to Tell?" for more tips.

One terrific tool that's dedicated to ferreting out and destroying Trojan horses is MooSoft's The Cleaner. It works in all current versions of Windows, searches for over 1800 Trojan horses, checks inside zipped files, and is updated regularly. Grab a trial copy from our Downloads library.

Dig this: Have you ever wondered what happens (drum roll, please) When Good Planes Go Bad?

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