Rootkits are becoming more prevalent and difficult to detect, and security vendor McAfee says the blame falls squarely on the open source community.

In its "Rootkits" report being published today, McAfee says the number of rootkits it has collected as malware samples has jumped ninefold this quarter compared with the same quarter a year ago. Almost all the rootkits McAfee has identified are intended to hide other code (such as spyware or bots) or conceal processes running in Windows systems.

"The predominant reason for the growth in use of stealthy code is because of sites like Rootkit.com," says Stuart McClure, senior vice president of global threats at McAfee

Rootkit.com's 41,533 members do post rootkit source code anonymously, then discuss and share the open source code. But it's naïve to say the Web site exists for malicious purposes, contends Greg Hoglund, CEO of security firm HBGary and operator of Rootkit.

"It's there to educate people," says Hoglund, who's also the co-author with James Butler of the book Rootkits: Subverting the Windows Kernel. "The site is devoted to the discussion of rootkits. It's a great resource for anti-virus companies and others. Without it, they'd be far behind in their understanding of rootkits."

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No one with a profoundly malicious intent would post his rootkit on the site, because it would be publicly analyzed for detection purposes, Hoglund says. He concedes, however, that out of the tens of thousands of Rootkit participants, there are bound to be those whose intent is to exploit rather than learn.

Anti-virus vendor Trend Micro says the Rootkit Web site cuts both ways.

"We need those open source people," says David Perry, global director of education at Trend Micro. "They uncover things. It's a laboratory of computer science. They demand the intellectual right to discuss this."

That said, Perry notes there are a lot of hacker wannabes who would be drawn to using the Rootkit site "as one-stop shopping for them to pick up the tools."

Designing a rootkit is a complex programming process. Hoglund says there are probably no more than 20 or 30 main types today, along with a wide number of variants.

Detecting rootkits has become a software research frontier, but eradicating them and what they hide is proving even more difficult.