Malicious Bots Hide Using Rootkit Code

Experts warn that "Rootbots" are emerging as a threat: remote control bots that borrow stealth features from rootkits to creep in undetected.

Computer viruses and remote control programs called bots are adopting features from stealthy programs called rootkits to avoid detection, according to researchers at Finnish anti-virus software company F-Secure.

New versions of Rbot, a malicious and ubiquitous remote control program, have features copied and pasted from a well known open-source rootkit called FU. The new features make Rbot invisible to system monitoring tools.

This is just the latest example of malicious programs borrowing strategies used by rootkits to evade detection on systems they infect, said Mikko Hyppönen, manager of anti-virus research at F-Secure Corp.

New versions of Rbot are identified almost daily, but recent variants come with a version of a software driver from FU, Hyppönen said.

When the driver is placed on an infected system, it allows Rbot to hide its process from the Windows task manager, or other task management tools that show users what programs are running on their Windows system.

The integration of FU with Rbot is crude and was probably done by an inexperienced hacker, or "script kiddie," who lifted the code wholesale from the FU source code, which was posted on the Internet by the rootkits author, Jamie Butler (aka "Fuzen") as a proof of concept.

/zimages/6/28571.gifClick here to read more about attempts at rootkit detection.

However, other malicious code authors are doing a more thorough job of tying rootkit features into their creations, Hyppönen said.

A recent variant of the Myfip worm, Myfip.h, incorporated features from FU that allowed it to manipulate data in the system kernel, or Windows core processing center, allowing it to hide its processes, he said.

The FU source code, available from Web sites like RootKit, is a rich source of information for malicious code writers. However, FU is not a true rootkit and doesnt try to evade detection.

That means that viruses and malicious programs that use FU components might still raise red flags from security programs that miss the virus processes running, but spot FU running on infected systems, he said.

Other virus authors seem to be catching on to tricks used by rootkit authors to avoid detection, also.

A recent version of the Sober worm, Sober.P, used a strategy called "I/O blocking" that doesnt prevent infected e-mails from being spotted, but can keep anti-virus products from detecting Sober.P on infected systems, according to experts.

Other e-mail worms have attempted to use I/O blocking, which Hyppönen called the "poor mans rootkit," to evade memory scans by anti-virus software. Sober.P improved on earlier attempts, and can even block scans by the powerful System account on infected systems, according to information posted on the Web site of Kaspersky Lab, a Russian anti-virus company.

Many anti-virus products dont do what is known as "on access" scanning in memory that would spot such tricks because the scans slow performance too much, said Vincent Gullotto, vice president of McAfee Inc. Avert.

"There are just so many programs going in and out of memory," he said.

/zimages/6/28571.gifRead more here about the latest Sober worm variant.

While Rbot, Myfip and Sober.P are still easy to spot, the convergence of rootkits, viruses and bots is bad news for computer users, Hyppönen said. More sophisticated rootkits such as "Hacker Defender" are much harder to spot, and could be coupled with bots or other malicious code to create potent threats, he said.

"Its almost scary. You can install [a program] on your hard drive and play around with it. You know its there, but no matter how hard you try to look for it, you wont see it," he said. "Potentially, one could write a bot that could not be detected at all."

F-Secure is testing a rootkit detection program called BlackLight that can spot some rootkits. Jamie Butler, author of the FU rootkit, has also released a free program called VICE that can spot FU, but most anti-virus companies dont have rootkit detection features in their products, he said.

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