Name :	Worm:W32/Zimuse.A
Detection Names :	Worm:W32/Zimuse.A Worm:W32/Zimuse.A Trojan.Generic.1729691
Aliases :	Win32/Zimuse.A (Other) Worm:Win32/Zumes.A!sys (Microsoft)
Category:	Malware
Type:	Worm
Platform:	W32
Date of Discovery:	January 25, 2010

A standalone malicious program which uses computer or network resources to make complete copies of itself. May include code or other malware to damage both the system and the network.

General
Zimuse is a family of worms that performs destructive overwrite of the Master Boot Record of disk drives on the infected system.


Arrival to the system
Zimuse.A arrives on the system either as a standalone file (possibly from a malicious download or e-mail) or by infected removable devices (e.g., USB sticks).

When executed, it will display a fake WinZip dialog box (see image below). This dialog box is a sham. Regardless of the user's subsequent interaction, the worm has already infected the system.




The following file operations will be performed on the system:

  • %windir%\system32\drivers\Mstart.sys [Worm.Zimuse.A]

  • %programfiles%\Dump\Dump.exe [nonmalicious component]

  • %windir%\system32\drivers\Mseu.sys [Worm.Zimuse.A]

  • %windir%\system32\mseus.exe [Worm.Zimuse.A]

  • %windir%\system32\tokset.dll [copy of itself]

  • %windir%\system32\ainf.inf [copy of the malicious autorun.inf]

  • %temp%\Regini.exe

  • %temp%\Dump.ini

  • %temp%\Mseu.ini

  • %temp%\mseus.ini

  • %temp%\Instdrv.exe

Launchpoint/Autostart
Uses registry launchpoints to ensure its components run or are loaded as services on every startup (see below).


Registry Changes
Creates these keys:

Sets these values:

EventMessageFile = %SystemRoot%\System32\Drivers\MSTART.SYS

TypesSupported = 7

Type = 1

Start = 3

ErrorControl = 1

ImagePath = \??\C:\WINDOWS\system32\Drivers\MSTART.SYS [Launchpoint: Service]

DisplayName = MSTART

Security =

Dump = C:\Program files\Dump\Dump.exe [Launchpoint: Run]

Type = 1

Start = 2

ErrorControl = 1

Tag = 1

Group = Extended base

Type = 272

Start = 2

ImagePath = System32\Mseus.exe [Launchpoint: Service]

ErrorControl = 0

DisplayName = Self extract service

ObjectName = LocalSystem

Description = Self extract archive decrypt

Infection
After a certain time period from the initial infection, the worm will infect removable drives inserted into the system by dropping a copy of itself named zipsetup.exe and an autorun.inf file as show below:

[autorun]
shellexecute=zipsetup.exe /H

Payload
After a further period of dormancy, the worm will trigger its payload, which overwrites the Master Boot Record of available drives on the system, and effectively crippling the file system and rendering data on the disk inaccessible except with specialist tools. The following dialog box will be displayed:

On next boot the system will be unbootable.


Removal
Manual removal:

1) Use task manager or process explorer to kill the "MSEUS.EXE" process.
2) Delete the following files:

  • %windir%\system32\drivers\Mstart.sys

  • %programfiles%\Dump\Dump.exe

  • %windir%\system32\drivers\Mseu.sys

  • %windir%\system32\mseus.exe

  • %windir%\system32\tokset.dll

  • %windir%\system32\ainf.inf

Delete as well any instances of zipsetup.exe on root folders as well as the autorun.inf

3) Delete the malicious registry entries, especially launchpoints as listed in the description.
4) Reboot system, run full scan.