Worried about the virulent Storm worm that has been buffeting the Internet with mass mailings?

Well, you should be concerned about the Storm worm, but a security researcher at IBM's Internet Security Systems told InformationWeek that the biggest malware threats aren't really the newest kids on the blocks. It's their older brothers.

Gunter Ollmann, director of security strategy at IBM's Internet Security Systems, said the most common malware attack today is coming from the Slammer worm. No, you didn't misread that last sentence. The Slammer worm, which hit in January 2003, is still working its way around the Internet and within corporate networks, according to Ollmann. And it's still spreading in a big way.

And Slammer isn't the only piece of old-time malware that is still wreaking havoc.

"The stuff [malware authors] wrote a while ago is still out there and still propagating and still infecting machines," he said. "Some have more infections now than they did when they were headline news. All those old vulnerabilities haven't all gone away."

Slammer, the worm that brought many networks to their knees by attacking Microsoft's SQL Server, is at the top of Ollmann's list of current malware problems.

"When we hear about the latest worm and zero-day, Slammer still beats them by a long shot," he added. "Slammer is still out there on a large number of infected hosts and it's still sending out malicious network traffic -- malicious packets... When people restore data after a crash, it probably is from an old system and it may not have the patches so it can easily be re-infected."

Another problem is that some users simply don't do the patching they should, while some users aren't even aware that Microsoft SQL Server is running on their desktop because it's common to several other applications. If they don't know it's there, they don't know to take care of it.

"All these old viruses are never going to go away," said Ollmann.