Symantec has found a new rootkit that hides from Windows XP on the hard drive's boot sector. Nasty stuff. A traditional rootkit installs as a driver while this new rootkit installs so that it controls the master boot record (MBR) before the operating system loads, said Symantec's security researcher Oliver Friedrichs, in a Computerworld story. This allows it to hide especially well - "unprecedented" is the term that Friedrich's uses to describe this threat. The rootkit is fine-tuned to work only on Windows XP systems. Vista users may remain protected because they should be explicitly asked to approve the installation of this MBR rootkit when a User Account Control warning pops up. This is because the rootkit requires administrative-level approval to install to the hard drive's master boot record.

The Computerworld story says:

"According to other researchers, including those with the SANS Institute's Internet Storm Center, Prevx Ltd. and a Polish analyst who uses the alias 'gmer,' the rootkit has infected several thousand PCs since mid-December, and is used to cloak a follow-on bank account-stealing Trojan horse from detection as well as to reinstall the identity thief if a security scanner somehow sniffs it out."

If the rootkit does find its way onto a system, you may be looking at a PC that cannot be repaired but has to be wiped clean. Symantec claims that its antivirus software fights the rootkit by identifying it as a Trojan named Mebroot when the rootkit attempts to install itself. Researchers also suggest checking to see if your PC's BIOS includes a MBR write-protection feature. If so, they advocate activating it.

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