The bigger problem, say some observers, is correcting the perception that the Mac platform is invulnerable. That notion has fostered a laissez-faire attitude toward security among Apple customers, says Intego's Peter James.

For years Apple has promoted the idea that Macs are far less vulnerable to malware and viruses than PCs are. As part of the "Get a Mac" television , actor John Hodgman (as the PC) says, "Last year, there were 114,000 known viruses for PCs." And Justin Long (as the Mac) replies, "PCs, but not Macs."

Mac users are faced with new threats that require new security precautions, James says. "They're faced with threats they've never seen before."

System administrator Steve Mallard says that many of the student Mac users for whom he provides help-desk services live in denial. Mallard, an IT manager for several state universities at the Tennessee Technology Center in Shelbyville, Tennessee, says students come to his staff with Mac problems and don't believe that their computers have been infected until shown the evidence.

Over the past few years, Mallard says, he has seen the percentage of infected Macs brought in by students jump from 1 to 15 percent.