Rootkit:Boot/Mebroot is a sophisticated program capable of replacing and controlling the infected system's Master Boot Record (MBR), then downloading and installing additional malware onto the infected system.
Windows includes tools to replace an infected MBR with a copy of the original, clean MBR. To do so:
Note: For further information on use of the 'fixmbr' command, please refer to the relevant Microsoft documentation.
For information on disinfecting and repairing the MBR, please see Master Boot Record (MBR) Repair. For more general information on disinfection, please see Removal Instructions.
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The MBR is the first physical sector of a computer system's hard drive and contains the first code loaded and executed from the drive during the boot process. A malicious program capable of subverting this critical sector is therefore able to control the entire system, while masking its own presence from the user.
The technical features of the Mebroot rootkit are discussed in further detail in the following Labs Weblog posts:
Mebroot is known to be distributed either by a trojan-downloader program found on malicious websites, or via an exploit.
Once installed, Mebroot silently downloads further programs onto the infected system; the downloaded malware appear to target online banking and other financial systems.