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DEFO.A-P

Overview


This destructive memory-resident boot virus infects the Master Boot Record (MBR) of hard disks set as drive C:\ and the boot sectors of floppy disks that are accessed.

Technical Details


File size: 512 bytes
File type: BOOT
Initial samples received date: 24 May 2010

NOTES:

Once the user starts or boots from an infected floppy disk, this malware sets up a copy of itself in high memory by allocating 8 KB of conventional memory. It also hooks INT 13 services, allowing it to infect floppy disks when accessed and then hides the infection.

It infects floppy disks using DOS disk manipulation services while it is resident in memory. It also infects the drive C:\ hard disks Master Boot Record (MBR).

This DOS boot virus uses 8 sectors to propagate. On drive C:\ hard disks, it overwrites the original MBR then hides the rest of the virus from cylinder 0, head 0, and sector 10 up to cylinder 0, head 0, and sector 17. It occupies a total of 8 sectors together with the original MBR located at cylinder 0, head 0 and sector 17.

On floppy disks, it modifies the Table Base of Parameters and defines an additional track with a nonstandard format. It does this to store the rest of the virus code together with the original boot sector. These sectors cannot be accessed by traditional methods of reading.

The following text is found in this virus body:

  • Runtime error 504D:5658

Solution


Minimum scan engine: 8.900
First VSAPI Pattern File: 7.192.13
First VSAPI Pattern Release Date: 24 May 2010

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Restore your system’s Master Boot Record (MBR)

To restore your system's Master Boot Record (MBR):

  1. Insert your Windows Installation CD into your CD-ROM drive or the USB flash drive then restart your computer.
  2. Press the restart button of your computer.
  3. When prompted, press any key to boot from the CD.
  4. When prompted on the Main Menu, type r to enter the Recovery Console.
    (For Windows 2000 users: After pressing r, type c to choose the Recovery Console on the repair options screen.)
  5. When prompted, type your administrator password to log in.
  6. Once logged in, type the drive that contains Windows in the command prompt that appears, and then press Enter.
  7. Type the following then press Enter:
    fixmbr {affected drive}
    (Note: The affected drive is the bootable drive that this malware/grayware has affected. If no device is specified, the MBR will be written in the primary boot drive.)
  8. Type exit to restart the system.


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Analysis By: Sabrina Lei Sioting

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