As for future targets, the Macintosh is likely to see still more action. Adding even more temptation for the virus-writing underworld, the Mac is now using Intel chips. This allowed Apple to come out with software called Boot Camp (www.apple.com/macosx/bootcamp), a free download that allows users to boot their Macintosh computers into either Mac OS X or Windows. I think it won't be long before the architects of digital disease are freely distributing equal opportunity malware that can infect Mac OS X, Windows and Linux -- sometimes zapping a couple of targets on the same piece of hardware.

One final note regarding keeping heterogeneous networks virus-free: Malware is often written to take advantage of flaws in programming. Flaws affect every operating system, so regular patching of your Windows, Linux and Mac machines remains paramount. When searching for a patch management tool for your heterogeneous environment, look for one that covers more than one operating system.

Douglas Schweitzer is a freelance writer and Internet security specialist in Nesconset, N.Y. He can be reached at dougneak@juno.com.