The Conficker botnet compromised an estimated seven million plus Windows PCs around the world at its peak. Seven million is obviously much larger than 600,000, but Windows also has a significantly higher number of PCs in use around the world.

According to current , Mac OS X is the number two desktop OS with 6.54 percent market share. Windows, on the other hand, accounts for 92.48 percent of the market. Based on market share, the Flashback Trojan botnet is equivalent to a Windows botnet of nearly 8.5 million PCs. That makes it an even larger threat than Conficker--just on a much smaller platform.

The Flashback Trojan is actually a misnomer at this point. It was a Trojan horse when it was originally discovered last year. A Trojan horse--as the historical reference implies--is malware that is disguised as something benign. The original threat masqueraded as an update for Adobe Flash that compromised machines when executed.

The current version, however, is more of a drive-by download threat. It , or passwords. If a user visits a malicious or compromised website, the Flashback malware runs automatically and vulnerable systems are infected.

A malware attack such as this has even greater odds of success on Mac OS X than it does on a Windows system. The Mac OS X system itself is not less secure or prone to infection than Windows per se, but the Mac culture is conditioned to believe the OS is virtually invulnerable. Fewer users have any security software installed to protect their Mac OS X systems, and Mac OS X users are more likely to click links and open files without thinking twice.