Analysis by: Cris Nowell Pantanilla
ALIASES:

Virus.Boot.Anticmos [Kaspersky], Virus:DOS/AntiCMOS.A [Microsoft]

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Others

  • Destructiveness: Yes

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

This malware deletes or modifies the CMOS setup information upon boot from infected floppy disk.

It also writes to critical sectors of an infected system's Drive C:\ making the drive inaccessible thereafter.

  TECHNICAL DETAILS

File Size: 512 bytes
File Type: BOOT
Initial Samples Received Date: 07 Mar 2000
Payload: Renders drive inaccessible

NOTES:

This malware deletes or modifies the CMOS setup information upon boot from infected floppy disk.

This malware decreases the available memory of an infected system by 2K Bytes and sets itself in the allocated area to become memory resident.

It hooks INT 13H and saves the original address of this interrupt in its virus code.

It sends garbage codes at address 42,43 and hence trashing the CMOS RAM via a port 70.

This malware also writes to critical sectors of an infected system's Drive C:\ making the drive inaccessible thereafter.

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 0.668.00
FIRST VSAPI PATTERN DATE: 07 Mar 2000

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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