Sept. 4 started out as a normal workday for Kevin Ma. By noon it was pure chaos.
The Blaster computer virus had taken down corporate computer networks across the country, and Mr. Ma, a computer consultant for Microtech Services in Boston, was among those charged with containing the virus, limiting its damage, and wiping it out.
Blaster, which Ma says "hammered" him and his colleagues, was one of 52 new viruses discovered this month, five of them major.
If you're like most computer users, you don't have Ma to come to rescue your home computer from the hundreds of damaging programs with names like Blaster, SoBig, Lovegate, and Klez.
And with high-speed Internet access linking millions of Americans, home computers are more vulnerable than ever.
Since viruses multiply exponentially through as many computers as possible, enlisting home users to stop their spread is crucial to reducing the overall impact of viruses, says David Perry, global director of education at TrendMicrosystems, an Internet-security company in Orange, Calif.
For all the disruption on corporate networks this month, businesses are generally much better protected than home users, says Mr. Perry.
In fact, the computer that took down the Microtech Services network was a laptop that had picked up a virus on the user's home network.
When dealing with viruses, there is no substitute for knowing what to watch out for and how to keep your computer current. "It's no different from knowing 30 years ago whether your car needed regular or unleaded gas," says Perry.
A few basics:
• A "virus" is simply any piece of computer code that automatically replicates itself. "The vast majority of dangerous content comes as e-mail attachments," says Chuck Adams, chief security officer with Netsolve, a computer-security firm in Waltham, Mass. They can also come through contact with Web pages.
• A "trojan" is an e-mail designed to trick users into opening it and launching a virus. Most often these, too, come as e-mail attachments. Though most Internet service providers now block the most dangerous attachments, experts warn against opening any attachment from an address you don't recognize.
• A "worm" is a more malicious type of computer code, because it doesn't require a user to do anything. Any time a computer is on the Internet, a worm can get in and run, causing anything from so-called "denial-of-service attacks" that bring the Internet to its knees, to deleting all the data on your hard drive.
Unfortunately, staying safe from computer viruses is now largely a reactive process, says Perry. Software companies such as Microsoft fix security holes after they discover them, and distribute the fixes, usually within hours. Corporate servers are designed to automatically look for these patches and install them. Home users should set their operating systems to do the same.
Good virus protection starts with installing antivirus software from one of the big three antivirus companies: Norton, McAfee, and TrendMicro. For anti- virus software to do any good, it has to have up-to-date virus definitions, which means you have to pay for the software and a subscription to keep receiving the latest list of viruses. A disk borrowed from your uncle or grandson probably won't help.
These definitions should be updated every time the computer is connected to the Internet. Make sure the antivirus software is set to scan every file as it comes in to your computer via e-mail, disks, even instant messaging. Also set such software to scan the entire hard drive for viruses at least three times a week, says Adam Kolawa, chairman of Parasoft, a company whose mission is to teach software companies to write more secure code.
Be especially careful of attachments in any format, such as Microsoft Word or Excel, capable of running scripts, says Mr. Kolawa. Set e-mail software to prompt you before opening attachments. And check e-mail programs to ensure that they don't "preview" messages - opening them automatically in small windows before you can eye the subject line.
To help thwart invading worms, say experts, you need to keep your computer's operating system current with patches, which rewrite sections of software to guard the key "kernel" code that controls the data on your hard drive. (In the process, they sometimes cause other features to fail, says Kolawa, but that's better than getting viruses.)
To keep hackers out of your machine, use a firewall. This can be simple software, such as McAfee or Zone Labs' ZoneAlarm, or a hardware device - such as a router, used for setting up a home network. Most firewalls can be customized to allow types of traffic that you wish to accept. After that, the antivirus software takes over the protection.
Turning off your computer or disconnecting from the Internet will minimize your exposure to viruses, hackers, and worms. DSL service requires you to connect before you surf; cable modems don't.
The best way to avoid viruses is to avoid questionable content. That includes places you might visit on the Web. If the knowledgeable relative you ask for help on all of this is your 12-year-old grandson, you might want to make sure he doesn't just fix up your computer so he can upgrade his music library on the Web. Music- and movie-sharing sites like Kazaa and Limewire, experts point out, have been known to harbor viruses.
Likewise, be wary of following Web links in an e-mail message unless you know the site to which they lead.
What should you do right now to protect your PC? The following 10 tips are recommended by Adam Kolawa, chief executive officer of Parasoft Corp., a Monrovia, Calif., firm that helps companies eliminate and prevent software errors.
Consult a computer retailer or the maker of an antivirus software product, such as Norton, for help in implementing these steps:
• Install a legal copy of an antivirus program, and keep it current through a subscription, so that it will recognize the latest "virus definitions."
• Set your computer's operating system to regularly download and update those virus definitions.
• Set Windows to automatically receive and install operating-system "patches" that can plug security holes in the software.
• Set antivirus software to scan all e-mail, Web pages, and instant-messaging traffic for viruses.
• Use the antivirus software to scan your hard drive for viruses at least three times a week.
• Don't open any attachments from any e-mail addresses you don't recognize.
• If you have high-speed Internet access, install a software firewall on your computer. (A hardware firewall is even better.)
• Never download anything from a website you don't know is reputable.
• Beware of e-mails that use Java or Active-X scripts (identified by moving, dancing, or interactive content).
• Clean out any "cookies" (which track your Web visits) from your browser.