New variant of mebroot detected that is harder to find and destroy

Marco Giuliani, virus researcher at Prevx, claimed that the original variant was designed to be hard to detect, and the new variant ‘is yet more tricky to be detected'.

Giuliani said: “Master Boot Record (MBR) is still the main target, but the way it hides itself from security products is somehow impressive.

“The new version of MBR rootkit is smart enough to give researchers some bad days, due to improved hooking techniques and spaghetti code. The rootkit is still using IRP hooks but in a smarter way.”

He claimed that the new variant does not hook the disk.sys driver, it goes deeper to check which is the lower device, to which the device is attached to, and then hooks on to that.

Jacques Erasmus, director of malware research at Prevx, claimed that the previous incarnation used the same technique but at a higher level, so it was easier to detect and remove.

He said: “Now it looks fine but it has got the rootkit mode that injects a malicious piece of code into a running process that steals passwords and banking details. As there are no files created on the hard disk it is hard to find, and every time the computer boots it loads itself.”

Giuliani said: “This hook, used to hide the MBR, is set on the fly every time the rootkit catches an attempt to read the MBR by opening a handle to the disk. Then, when the handle is closed, the hook is removed. Everything will look clean, because of no visible hooks.

“To understand when someone is opening a handle to the disk the rootkit uses a technique called Direct Kernel Object Hooking. This technique, already known since some time but used only by a few rootkits because of its complexity, attacks Windows Kernel Objects' methods. By doing so, attackers can control and alternate the OS from one of the best places.”