Microsoft is telling Windows users that they'll have to reinstall the operating system if they get infected with a new rootkit that hides in the machine's boot sector.
A new variant of a Trojan Microsoft calls "Popureb" digs so deeply into the system that the only way to eradicate it is to return Windows to its out-of-the-box configuration, Chun Feng, an engineer with the Microsoft Malware Protection Center (MMPC), said last week on the group's
blog .
"If your system does get infected with Trojan:Win32/Popureb.E, we advise you to fix the MBR and then use a recovery CD to restore your system to a pre-infected state," said Feng.
A recovery disc returns Windows to its factory settings.
Malware like Popureb overwrites the hard drive's master boot record (MBR), the first sector -- sector 0 -- where code is stored to bootstrap the operating system after the computer's BIOS does its start-up checks. Because it hides on the MBR, the rootkit is effectively invisible to both the operating system and security software.
According to Feng, Popureb detects write operations aimed at the MBR -- operations designed to scrub the MBR or other disk sectors containing attack code -- and then swaps out the write operation with a read operation.
Although the operation will seem to succeed, the new data is not actually written to the disk. In other words, the cleaning process will have failed.
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