1. Symantec/
  2. Security Response/
  3. W32.Mimail.A@mm


Risk Level 2: Low

August 1, 2003
February 13, 2007 12:04:22 PM
Also Known As:
WORM_MIMAIL.A [Trend], W32/Mimail@MM [McAfee], Win32.Mimail.A [CA], W32/Mimail-A [Sophos], I-Worm.Mimail [Kaspersky]
Systems Affected:
CVE References:
CAN-2002-0980 CAN-2002-0077

When W32.Mimail.A@mm is run, it does the following:
  1. Copies itself to %Windir%\Videodrv.exe.

  2. Adds the value:


    to the registry key:


    so that W32.Mimail.A@mm runs when you start Windows.

  3. Collects email addresses from all the files except those with the following file extensions:

  4. Writes all the email addresses to the file, %Windir%\eml.tmp, if it can resolve www.google.com to any IP address.

  5. Captures text from specific windows and sends the data to email addresses that the worm contains.

  6. Sends email messages using its own SMTP engine. For each email address to which the worm wants to send itself, it will:
    • Look up the MX record for the domain name using the DNS server of the current host. If a DNS server is not found, it will default to
    • Acquire the mail server associated with that particular domain.
    • Directly contact the destination server.

      The email has the following characteristics:

      From: admin@<current domain> (The from address may be spoofed to appear that it is coming from the current domain)

      Subject: your account [random string]

      Hello there,
      I would like to inform you about important information regarding your email address. This email address will be expiring. Please read attachment for details.

      Best regards,

      Attachment: Message.zip

  7. Message.zip contains only one file, Message.htm, which uses a code base exploit to create a copy of the worm named Foo.exe in the Temporary Internet Files folder, and then runs it. The compression method of this file inside the zip file is stored so that compression is not used at all.

    Information about this vulnerability and a Microsoft patch is located at: http://support.microsoft.com/default.aspx?scid=kb;en-us;330994. We encourage system administrators to apply the Microsoft patch to prevent infection by this worm.

  8. When the HTML file is executed, it will cause the following registry key to be created:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Code Store Database\Distribution Units\{11111111-1111-1111-1111-111111111111}

  9. The worm creates two additional files in the %Windir% folder:
    • Zip.tmp: This is a temporary copy of message.zip (30,079 bytes).
    • Exe.tmp: This is a temporary copy of message.html (29,957 bytes).


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: Atli Gudmundsson
Summary| Technical Details| Removal

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