1. Symantec/
  2. Security Response/
  3. W32.Zimuse


Risk Level 1: Very Low

January 23, 2010
January 27, 2010 7:12:55 AM
Also Known As:
W32/Mseus-A [Sophos], W32/Zimuse [McAfee], W32/Zimuse.A [F-Secure], Mseus.A [Panda Software], WORM_ZIMUS.A [Trend]
Infection Length:
228,352 bytes
Systems Affected:
It reportedly arrives on the compromised computer as a Slovakian language IQ test as the following file:

Once executed, the worm drops the following files:
  • %ProgramFiles%\Dump\Dump.exe
  • %System%\drivers\Mseu.sys
  • %System%\drivers\Mstart.sys
  • %System%\ainf.inf
  • %System%\mseus.exe
  • %System%\tokset.dll

It drops the following nonmalicious files into C:\IQTEST and then opens an Explorer window and displays the C:\IQTEST folder contents:
  • C:\IQTEST\Iqtest.exe (clean version of the IQ test)
  • C:\IQTEST\Readme.txt

Note: Both the clean IQ test program and the threat use the same icon:

The program c:\iqtest\Iqtest.exe is a clean program that looks like this:

The worm then deletes itself.

After a predetermined number of days the worm copies itself as zipsetup.exe to the following drives and to the first 9 physical drives:
  • C:
  • D:
  • E:
  • F:
  • G:
  • H:
  • I:
  • J:
The worm creates the following registry entry, so that it runs every time Windows starts:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\"Dump" = "%ProgramFiles%\Dump\Dump.exe"

It creates new services with the following characteristics:
Service Name: Mseu
Display Name:
Startup Type:
Image Path:

Service Name: Mstart
Display Name:
Startup Type:
Image Path:

Service Name: UnzipService
Display Name:
Startup Type:

Service Name: Self Extract Service
Display Name:
Self Extract Service
Startup Type:

The worm creates the services by adding entries to the following registry subkeys:
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Mseu
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\UnzipService

It spreads through removable drives as the file zipsetup.exe and it is also shared online as the following program:

It also copies the following file so that it runs when the removable devices are accessed:

After a predetermined amount of time the threat will attempt to delete the following files:
  • C:\System Volume Information
  • D:\System Volume Information
  • E:\System Volume Information
  • F:\System Volume Information
  • G:\System Volume Information
  • H:\System Volume Information
  • I:\System Volume Information
  • J:\System Volume Information
  • C:\Documents and Settings\Administrator\My Documents
  • D:\Documents and Settings\Administrator\My Documents
  • E:\Documents and Settings\Administrator\My Documents
  • F:\Documents and Settings\Administrator\My Documents
  • G:\Documents and Settings\Administrator\My Documents
  • H:\Documents and Settings\Administrator\My Documents
  • I:\Documents and Settings\Administrator\My Documents
  • J:\Documents and Settings\Administrator\My Documents
  • C:\Users\Administrator
  • D:\Users\Administrator
  • E:\Users\Administrator
  • F:\Users\Administrator
  • G:\Users\Administrator
  • H:\Users\Administrator
  • I:\Users\Administrator
  • J:\Users\Administrator
  • C:\Documents and Settings
  • D:\Documents and Settings
  • E:\Documents and Settings
  • F:\Documents and Settings
  • G:\Documents and Settings
  • H:\Documents and Settings
  • I:\Documents and Settings
  • J:\Documents and Settings
  • C:\Users
  • D:\Users
  • E:\Users
  • F:\Users
  • G:\Users
  • H:\Users
  • I:\Users
  • J:\Users
  • C:\NTLDR
  • C:\NTLDR

The threat also deletes all system restore points by deleting the following folders:
  • C:\System Volume Information
  • D:\System Volume Information
  • E:\System Volume Information
  • F:\System Volume Information
  • G:\System Volume Information
  • H:\System Volume Information
  • I:\System Volume Information
  • J:\System Volume Information

After a predetermined number of days, it displays the following message:

It will also attempt to overwrite the beginning of the disk in order to overwrite the master boot record (MBR), thereby not allowing the compromised computer to be restarted.

When restarted, the system may display the message "Operating System not found".


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.
Writeup By: Liam O Murchu
Summary| Technical Details| Removal

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