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Malicious Software Encyclopedia: Win32/Bagle

Published: March 25, 2009

Win32/Bagle is a family of mass-mailing worms that targets certain versions of Microsoft Windows. The worm spreads primarily through e-mail, though some variants also spread through peer-to-peer networks. The worm acts as a backdoor Trojan, allowing an attacker to access a computer that it has infected. The backdoor can be used to distribute other malicious software. Some variants of Win32/Bagle infect executable files.

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On This Page
Threat OverviewThreat Overview
Aliases (Also Known As)Aliases (Also Known As)
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

Threat Overview

Class/typeWorm - Mass Mailer
Trojan - Backdoor
DiscoveredJanuary 18, 2004
CirculatingYes
Child variantsWin32/Bagle.AX@mm
Win32/Bagle.BA@mm
Worm:Win32/Bagle.AX@mm!CME473
Worm:Win32/Bagle.BA@mm!CME477
Affected operating systems
Affected software Not specified
Infection ratingMedium
Recovery difficultyModerate
Damage ratingMedium
Transmission ratingHigh

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):

  • CA: Win32.Bagle
  • McAfee: W32/Bagle@MM
  • Symantec: W32.Beagle.gen
  • Trend Micro: WORM_BAGLE

    • Learn more about the Microsoft Virus Information Alliance.

    Technical Analysis

    Win32/Bagle spreads primarily by attaching itself to e-mails it sends to addresses that it finds on an infected computer. Many Win32/Bagle variants attach a password-protected compressed file. The e-mail subject line or message body may contain the password.
     
    When Win32/Bagle runs, it copies itself to the %System% or %Temp% directory, and possibly other random directories. It creates a value in one of the following registry keys:
    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    The registry value activates the worm whenever Windows starts.
     
    Win32/Bagle monitors a TCP port for instructions from remote attackers. It might inject code into explorer.exe and run the file. It might also terminate numerous security-related processes. 

    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 for all your installed software.
    • Use up-to-date antivirus software.
    • Use caution when opening attachments and accepting file transfers.
    • Use caution when clicking on links to web pages.
    • Avoid downloading pirated software.
    • Protect yourself against social engineering attacks.
    • Use strong passwords.
    Enable a firewall on your computer
    Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.
    To turn on the Windows Firewall in Windows Vista
    1. Click Start, and click Control Panel.
    2. Click Security.
    3. Click Turn Windows Firewall on or off.
    4. Select On.
    5. Click OK.
    To turn on the Internet Connection Firewall in Windows XP
    1. Click Start, and click Control Panel.
    2. Click Network and Internet Connections. If you do not see Network and Internet Connections, click Switch to Category View.
    3. Click Change Windows Firewall Settings.
    4. Select On.
    5. Click OK.
    Get the latest computer updates
    Updates help protect your computer from viruses, worms, and other threats as they are discovered. It is important to install updates for all the software that is installed in your computer. These are usually available from vendor websites.
     
    You can use the Automatic Updates feature in Windows to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
    To turn on Automatic Updates in Windows Vista
    1. Click Start, and click Control Panel. 
    2. Click System and Maintainance.
    3. Click Windows Updates.
    4. Select a setting. Microsoft recommends selecting Install updates automatically and choose a time that is convenient for you. If you do not choose Automatic, but you choose to be notified when updates are ready, a notification balloon appears when new downloads are available to install. Click the notification balloon to review and install the updates.
    To turn on Automatic Updates in Windows XP
    1. Click Start, and click Control Panel. 
    2. Click System.
    3. Click Automatic Updates.
    4. Select a setting. Microsoft recommends selecting Automatic. If you do not choose Automatic, but you choose to be notified when updates are ready, a notification balloon appears when new downloads are available to install. Click the notification balloon to review and install the updates.
    Use up-to-date antivirus software
    Most antivirus software can detect and prevent infection by known malicious software. To help protect you from infection, you should always run antivirus software that is updated with the latest signature files. Antivirus software is available from several sources. For more information, see http://www.microsoft.com/protect/computer/viruses/vista.mspx.
    Use caution when opening attachments and accepting file transfers
    Exercise caution with e-mail and attachments received from unknown sources, or received unexpectedly from known sources.  Use extreme caution when accepting file transfers from known or unknown sources.
    Use caution when clicking on links to Web pages
    Exercise caution with links to web pages that you receive from unknown sources, especially if the links are to a Web page that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your system simply by visiting a Web page with harmful content.
    Avoid downloading pirated software
    Threats may also be bundled with software and files that are available for download on various torrent sites. Downloading "cracked" or "pirated" software from these sites carries not only the risk of being infected with malware, but is also illegal. For more information, see 'The risks of obtaining and using pirated software'.
    Protect yourself from social engineering attacks
    While attackers may attempt to exploit vulnerabilities in hardware or software in order to compromise a system, they also attempt to exploit vulnerabilities in human behavior in order to do the same. When an attacker attempts to take advantage of human behavior in order to persuade the affected user to perform an action of the attacker's choice, it is known as 'social engineering'. Essentially, social engineering is an attack against the human interface of the targeted system. For more information, see 'What is social engineering?'.
    Use Strong Passwords
    Attackers may try to gain access to your Windows account by guessing your password. It is therefore important that you use a strong password – one that cannot be easily guessed by an attacker. A strong password is one that has at least 8 characters, and combines letters, numbers, and symbols. For more information, see http://www.microsoft.com/protect/yourself/password/create.mspx.

    How to Tell If Your Computer Is Infected

    If your computer is infected by Win32/Bagle, you may not notice any apparent symptoms, or you may notice crashes or slowdowns during normal operation.

    How to Recover from Infection

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

    Manual Recovery

    Manual removal is not recommended for this threat. To detect and remove this threat and other malicious software that may have been installed, run a full-system scan with an up-to-date antivirus product such as the Microsoft online scanner (http://safety.live.com). For more information, see http://www.microsoft.com/protect/computer/viruses/vista.mspx.

    Transmission Methods

    MethodDescription
    Mass Mailer
    Social Engineering

    Payload Information

    Payload typeTriggerDescription
    Compromises Security
    Creates files
    Sends e-mails
    Degrades Performance

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