Internet advertisers want to bombard you with pop-up ads. Hackers might need to “borrow” your computer to mount an attack on another server. Or they might be “phishing” for credit card numbers. Or not. A good percentage of Internet mischief is nothing more than kids somewhere testing their programming chops. No matter what they want, your information is at risk.

Get thee behind a firewall. Windows XP SP2 enables a firewall by default. Zone Alarm ( www.zonealarm.com) is free. Hardware routers with built-in firewalls cost less than $100. There is no excuse for not protecting your information (and that of your clients) with a firewall.

The evils of HTML e-mail. Hyper-Text Markup Language (HTML) e-mail looks nice, but it can deliver such things as “Web bugs” (as in “bugging” your phone line), which connect with a remote Web server, allowing it to deposit a tracking cookie on your computer just as if you had surfed to the site on your own. Outlook 2003 offers the option of converting all incoming e-mail to plain ASCII text.

Scan and scan alike. Nearly every anti-virus and anti-spyware utility worth mentioning is available for download at www.computercops.biz. But some malware is so aggressive that even the most sophisticated scanners won't catch all of it. HiJack This (available at the above site) creates a log of everything running on your computer and is often the only way to figure out the problem.

Turning back time. Symantec's ( www.symantec.com) GoBack ($40) lets you turn back the clock to just before you got infected. Norton Ghost ($70) allows you to make a clean “image” of your hard drive, complete with operating system, applications, and settings. If disaster strikes, re-install the drive image, and you're malware-free. —Joe Stoddard is a process/technology consultant to the building industry. Reach him at www.mountainconsulting.com.