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Security essentials, and updates, can inoculate your computer

In olden times, the best home security consisted of a deep moat around a castle with only a drawbridge for access.

Primitive? Yes. But as computer worms and other forms of high-tech intrusion become more sophisticated, tactics from the Dark Ages are coming to the fore, only this time, the castle is your home computer and the moat is software called a firewall.

A firewall, simply put, monitors the Internet-related data traveling in and out of your computer. It lets in only certain kinds of traffic, which are identified by the electronic doors, or "ports," they use to enter your computer.

A firewall can raise the drawbridge on a port, if necessary, to keep out unwanted and potentially harmful traffic. Such a program is particularly important if you have high-speed, always-on Internet access via a cable or phone-based DSL connection.

Network ICE, recently acquired by Internet Security Systems, makes a popular Windows firewall called BlackICE Defender. ZoneLabs offers its ZoneAlarm in free and paid Windows versions. Symantec sells the Norton Internet Security suite for both Windows and Macintosh.

Other firewalls are available for Windows and Macintosh machines. Reviews can be found on sites such as

You may need more than just a firewall. So-called intrusion-detection software can examine the contents of data packets entering your computer, something a firewall alone cannot do, said Chris Klaus, Internet Security Systems founder and chief technology officer.

GFI Ltd. sells LANguard File Integrity Checker for Windows. The aforementioned BlackICE Defender is an example of an all-in-one product, incorporating an intrusion-detection system as well as a firewall.

For additional security, keep these tips in mind:

_ E-mail precautions. Be cautious about opening e-mail attachments, even those that appear to come from people you know, says Steve Trilling, director of research for Symantec's Anti-Virus Research Center in southern California. Many viruses piggyback on computers' address books to propagate themselves quickly.

_ Password protection. To combat password theft, Trilling recommends making passwords as long as possible. Many hackers use cracking programs that incorporate English dictionaries so use uncommon or foreign-language words. Better yet, use random combinations of numbers and letters in upper and lower cases.

_ Software maintenance. Users should monitor their systems and regularly visit the home pages of providers of their operating system, Web browser and e-mail program for software patches and other security-related updates, said Mike Endrizzi, chief executive of InterSec Communications, a Minnesota computer-security company.

_ Update virus software. Do so regularly _ weekly, if not daily. The majority of computer users still don't update their systems for weeks, if not months, security experts complain. Antivirus companies such as Symantec discover 10 to 15 viruses a day. "It's a people problem, not a technology problem," Endrizzi said.