This column often devotes a good bit of space to computer security and online privacy. But the tips have always appeared piecemeal, so it's difficult to remember (even for me) everything you should be doing to protect your PC and its data. This month I've assembled a safety checklist that gives you the big picture. Though it's not the final word on each of the topics presented, it will provide you with an overview of what you need to know and the steps you must take to avoid e-mail viruses, deter snoops, and halt attempts to hack into your PC or network. (For even more information on this broad subject, read the article " Internet Fixes.")

Block Hackers and Viruses

Connecting your PC to the Internet without using a firewall and antivirus software is like leaving your front door unlocked when you go on vacation--if you're lucky you'll come home to find that all is well, but it's still risky.

Install a firewall on every computer: Even if you have a hardware firewall between your PC or network and the Internet, you should still install a software firewall. Although a hardware firewall can be set to block or allow all packets passing in and out through port 500, for example, it doesn't know which application initiated the communication on your system. A software firewall routinely queries you to confirm whether it should let an application communicate over a given port (see FIGURE 1), so you can tell it that MyCoolInstantMessenger.exe is allowed to use the port but NastyTrojanHorse.exe isn't.

Use a bidirectional firewall: The firewall in Windows XP is better than nothing, but not much better. Free firewalls such as Zone Labs' ZoneAlarm 3 and Sygate's Personal Firewall 5 monitor and control both inbound and outbound network traffic, allowing them to block connections initiated on your PC by the aforementioned NastyTrojanHorse.exe or any real-life backdoor program.

Don't skip the antivirus: If you're not using antivirus software right now, stop what you're doing, go get some, and then continue reading after you've installed it. If you use Windows, not using antivirus software is simply irresponsible because of the high volume of viruses that target any version of this OS. Even if you think you know how to avoid viruses, you may eventually get nailed by one that employs a new and unexpected technique. If you get infected, chances are you'll infect the family members, friends, colleagues, and others who are in your address book, too.

If you don't want to shell out for a top commercial package like Symantec's Norton AntiVirus, at least download Grisoft's free AVG 6 Anti-Virus System. AVG isn't great at catching the latest known in-the-wild viruses, according to UK-based antivirus journal Virus Bulletin. Because of this shortcoming, using AVG could be just as bad as having no antivirus protection if you blindly launch every e-mail attachment that slithers into your in-box. However, if you have other prevention methods in your tool bag (such as a script-resistant e-mail program and a healthy distrust of e-mail attachments), it will at least prevent you from being nailed by those viruses that perennially come around. I've been using AVG for more than a year with great success and a minimum of hassle, but it's a period I nevertheless consider an experiment in living dangerously.

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