But even software scans may not be enough to detect the Storm worm, according to Internet Security Systems' Corman.

FORBES: Zombie Storm Rising

More than other strains of malicious code, the Storm worm has proven itself difficult to outsmart since it was discovered in January 2007.

FORBES: Storm For Rent

"The Storm worm is patient, resilient, adaptive and invisible, " says Corman.

FORBES: Magazine Article

For nearly a year, cyber-security researchers have tracked the Storm worm as its malicious code spread across the Internet, drawing computers into a growing botnet of hijacked computers.

FORBES: Storm For Rent

Now, that zombie software is becoming more infectious and sophisticated: One strain in particular, the so-called "Storm worm, " has enslaved between 15 and 50 million PCs, by security researchers' estimates.

FORBES: Zombie Storm Rising

Even scarier, Storm's creators are actively attacking researchers who try to uncover the worm's secrets.

FORBES: Zombie Storm Rising