Click Here to Install Silverlight*
United StatesChange|All Microsoft Sites
Microsoft
Security 

Malicious Software Encyclopedia: Win32/Mimail

Published: June 14, 2005

W32/Mimail is a family of mass-mailing and network worms. The variants target several versions of Microsoft Windows. Mimail variants spread in various ways. Some spread through e-mail attachments. Some target computers that do not have Microsoft Security Bulletins MS02-015 and MS03-014 installed.  Some variants spread through peer-to-peer networks. Some variants gather and transmit user account numbers and passwords. Some variants launch denial of service (DoS) attacks against certain Web sites.

**

Related Links

•

Removal Tools - Microsoft

Glossary Terms

Click the term to get the definition from our Security Glossary.

•

Trojan horse

•

virus

•

worm

**
On This Page
Threat OverviewThreat Overview
Aliases (Also Known As)Aliases (Also Known As)
Related Security BulletinsRelated Security Bulletins
Technical AnalysisTechnical Analysis
How to Prevent InfectionHow to Prevent Infection
How to Tell If Your Computer Is InfectedHow to Tell If Your Computer Is Infected
How to Recover from InfectionHow to Recover from Infection
Transmission MethodsTransmission Methods
Payload InformationPayload Information
Modified Registry EntriesModified Registry Entries

Threat Overview

Class/typeWorm - Mass Mailer
Worm - Network
DiscoveredAugust 1, 2003
CirculatingYes
Affected operating systemsWindows NT 4.0
Windows 95
Windows 2000
Windows XP
Windows Server 2003
Affected software Not specified
Infection ratingMedium
Recovery difficultyModerate
Damage ratingMedium
Transmission ratingMedium

Aliases (Also Known As)

Different antivirus vendors may be using different names to refer to this malicious software. Here are some of the names currently in use by antivirus software vendors participating in the Microsoft Virus Information Alliance (VIA):

  • McAfee: W32/Mimail@MM
  • Sophos: W32/Mimail
  • Symantec: W32.Mimail
  • Trend Micro: WORM_MIMAIL

    • Learn more about the Microsoft Virus Information Alliance.

    Related Security Bulletins

    The following Microsoft Security bulletins are related to this issue:

  • MS02-015 - 28 March 2002 Cumulative Patch for Internet Explorer
  • MS03-014 - Cumulative Patch for Outlook Express (330994)

    • Technical Analysis

    Win32/Mimail variants spread in various ways. They can use mass mailings, peer-to-peer networks, or exploit the Windows vulnerabilities patched by MS02-015 and MS03-014.
     
    The mass-mailer variants gather e-mail addresses from the infected computer. The worm then sends itself as an e-mail attachment to the collected e-mail addresses. The worm file is often contained in an attached .zip file, and is activated when a user opens the attachment.
     
    Some variants gather user account numbers and passwords and send them to other Web sites. The worm may also launch denial of service (DoS) attacks against certain Web sites.
     
    Win32/Mimail worm variants usually modify the Windows registry so that the worm is activated every time Windows starts. The worm may also register itself as a Windows system service process so that it continues to run after the user logs off.

    How to Prevent Infection

    Take the following steps to help prevent infection on your system:
    • Enable a firewall on your computer.
    • Get the latest computer updates.
    • Use up-to-date antivirus software.
    • Use caution with unknown attachments.

    Enable a firewall on your computer

    Use a third-party firewall product or turn on the Microsoft Windows XP Internet Connection Firewall.
    To turn on the Internet Connection Firewall in Windows XP
    1. Click Start, and click Control Panel.
    2. Click Network and Internet Connections, and click Network Connections. If you do not see Network and Internet Connections, click Switch to Category View.
    3. Highlight a connection that you want to help protect, and click Change settings of this connection.
    4. Click Advanced, and select Protect my computer and network by limiting or preventing access to this computer from the Internet.
    5. Click OK.

    Get the latest computer updates

    Updates help protect your computer from viruses, worms, and other threats as they are discovered. You can use the Automatic Updates feature in Microsoft Windows XP to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
    To turn on Automatic Updates in Windows XP
    1. Click Start, and click Control Panel. 
    2. Click Performance and Maintenance. If you do not see Performance and Maintenance, click Switch to Category View.
    3. Click System.
    4. Click Automatic Updates, and select Keep my computer up to date.
    5. Select a setting. Microsoft recommends selecting Automatically download the updates, and install them on the schedule that I specify and setting a regular update time.
    6. If you choose to have Automatic Updates notify you in step 5, you will see a notification balloon when new downloads are available to install. Click the notification balloon to review and install updates.

    Use up-to-date antivirus software

    Most antivirus software can detect and prevent infection by known malicious software. You should always run antivirus software on your computer that is updated with the latest signature files to automatically help protect you from infection. If you don't have antivirus software installed, you can get it from one of several companies. For more information, see http://www.microsoft.com/athome/security/downloads/default.mspx

    Use caution with unknown attachments

    Use caution before opening unknown e-mail or IM attachments, even if you know the sender. If you cannot confirm with the sender that a message is valid and that an attachment is safe, delete the message immediately, and run up-to-date antivirus software to check your computer for viruses.

    Remove unneeded network shares

    Malicious software can often spread over network shares. Remove unneeded network shares that are mapped to your computer.
    To remove network shares in Windows XP
    1. On the Start menu, click My Computer.
    2. On the Tools menu, click Disconnect Network Drives…
    3. In the Disconnect Network Drives dialog box, click the drives to disconnect and click OK.

    How to Tell If Your Computer Is Infected

    There may be no readily apparent indications that your computer is infected with a Win32/Mimail variant. However, your computer may be infected with this worm if you find certain files and new registry values on your computer. See individual Mimail variant descriptions for more information.

    How to Recover from Infection

    Automatic Recovery
    To attempt to automatically remove this threat, run one of the following removal tools:

    Transmission Methods

    MethodDescription
    Mass MailerSends itself as an attachment to e-mail addresses on the infected computer.
    Social EngineeringActivates when the user opens an e-mail attachment or opens the worm file in a peer-to-peer file-sharing folder.
    Network SharesSpreads through peer-to-peer file-sharing networks, writing itself to file-sharing folders.

    Payload Information

    Payload typeTriggerDescription
    Creates files
    Infection
     
    Sends e-mails
    Execution
     
    Deletes files
    Execution
    Display something
    Execution
    Release information
    Execution

    Modified Registry Entries

    Changed registry entries
    Key
    Value name
    Old value
    New value

    © 2009 Microsoft Corporation. All rights reserved. Contact Us |Terms of Use |Trademarks |Privacy Statement