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Malicious Software Encyclopedia: Worm:Win32/Esbot.A

Published: September 12, 2005

Worm:Win32/Esbot.A is a network worm that targets computers running Microsoft Windows 2000 that do not have Microsoft Security Bulletin MS05-039 installed. The worm can also infect computers running other Windows operating systems if it is delivered through e-mail, instant messaging, or other routes. The worm has a backdoor component that connects to an IRC server to receive commands from attackers.

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Glossary Terms

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

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Trojan horse

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virus

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worm

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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
Changed ProcessesChanged Processes
Changed ServicesChanged Services
Affected PortsAffected Ports
Dropped FilesDropped Files

Threat Overview

Class/typeWorm - Network
Trojan - Backdoor
DiscoveredAugust 15, 2005
CirculatingYes
Affected operating systemsWindows 2000
Affected software Not specified
Infection ratingMedium
Recovery difficultyModerate
Damage ratingMedium
Transmission ratingLow

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.Esbot.A
  • F-secure: W32/Backdoor.EUR
  • McAfee: W32/IRCbot.gen
  • Sophos: Esbot.A
  • Symantec: Esbot.A
  • Trend Micro: BKDR_RBOT.BD

    • Learn more about the Microsoft Virus Information Alliance.

    Related Security Bulletins

    The following Microsoft Security bulletins are related to this issue:

  • MS05-039 - Vulnerability in Plug and Play Could Allow Remote Code Execution and Elevation of Privilege (899588)

    • Technical Analysis

    When Worm:Win32/Esbot.A runs, it takes the following actions:
    • Copies itself as a new file to <system folder>\mousebm.exe. 
    • Creates registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MouseBM
      This registers the worm as a service named mousebm. This service has display name "Mouse Button Monitor" and executable file name <system folder>\mousebm.exe.
    • Exits after starting worm service mousebm.exe. The service checks for the presence of a mutex named mousebm. If the mutex exists, the worm process mousebm.exe exits. If the mutex does not exist, the process takes the following actions:
      • Creates mutex mousebm to prevent multiple instances of the worm from running on the same computer.
      • Places data: N
        in value: EnableDCOM
        of registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLE
      • Places data: 1
        in value: restrictanonymous
        of registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
      • Injects its code into the explorer.exe process space and runs the injected code.
      • Scans randomly-selected IP addresses to exploit the Windows Plug-and-Play vulnerability described in Microsoft Security Bulletin MS05-039. The worm may begin scanning with a random address or an address based on the IP address of the infected computer; it then scans IP addresses consecutively.
      • Connects to a specific IRC server and channel to enable attackers to perform functions such as the following:
        • Download files.  
        • Run commands or executable files.
        • Collect information such as system information and file data.

    How to Prevent Infection

    Follow these 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.

    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  

    How to Tell If Your Computer Is Infected

    There are no readily apparent indications that your computer is infected with Backdoor:Win32/Esbot.A. However, the following symptoms may indicate that your computer is infected by this Trojan:
    • Presence of the file <system folder>\mousebm.exe.
    • The Processes tab in Windows Task Manager shows that mousebm.exe is running.
    • The executable file mousebm.exe is running as a service with display name "Mouse Button Monitor."

    How to Recover from Infection

    Manual Recovery

    To manually recover from infection by Worm:Win32/Esbot.A, follow these steps:
    1. Install Windows security update MS05-039.
    2. Disconnect from the Internet.
    3. Restart your computer in safe mode.
    4. Delete the registry key for the worm service.
    5. Delete the worm file.
    6. Restart your computer.
    7. Take steps to prevent re-infection.

    Install Windows security update MS05-039

    To install MS05-039 using Windows Update
    1. Go to the Windows Update Web site at windowsupdate.microsoft.com.
    2. On the Windows Update site, click Scan for Updates. Windows Update scans your computer and returns a list of critical updates, including service packs.
    3. In the Pick updates to install list, click Critical Updates and Service Packs. Windows Update creates a list of the updates appropriate for your computer, including MS05-039 if it is not installed. Critical updates are selected for download automatically.
    4. Click Review and install updates, and then click Install Now. You may need to restart your computer after installing the updates.

    Disconnect from the Internet

    To help ensure that your computer is not actively infecting other computers, disconnect it from the Internet before proceeding. Print this Web page or save a copy on your computer; then unplug your network cable and disable your wireless connection. You can reconnect to the Internet after completing these steps.

    Restart your computer in safe mode

    To start your the computer in safe mode
    1. Remove all floppy disks and CDs from your computer, and then restart your computer.
    2. When prompted, press F8. If Windows starts without displaying the Please select the operating system to start menu, restart your computer. Press F8 after the firmware POST process completes, but before Windows displays graphical output.
    3. From the Windows Advanced Options menu, select a safe mode option.

    Delete the registry key for the worm service

    Worm:Win32/Esbot.A creates a key in the Windows registry that registers the worm as a service. This entry should be deleted.
    To delete the registry key for the worm service
    1. On the Start menu, click Run.
    2. Type regedit and click OK.
    3. In the left pane, navigate to the key:
      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MouseBM
    4. Right-click the key and click Delete.
    5. Click Yes to confirm the deletion.
    6. Close the Registry Editor.

    Delete the worm file

    To delete the worm file from your computer
    1. Click Start, and click Run.
    2. In the Open field, type the name of the Windows system folder, for example, C:\Winnt\System32
    3. Click OK.
    4. Click Name to sort files by name.
    5. If mousebm.exe is in the list, delete it.
    6. On the Desktop, right-click the Recycle Bin and click Empty Recycle Bin.
    7. Click Yes.
    If deleting the file fails, follow these steps to verify that mousebm.exe is not running:
    1. Press CTRL+ALT+DEL once and click Task Manager.
    2. Click Processes and click Image Name to sort the running processes by name.
    3. Confirm that mousebm.exe is not in the list.

    Restart your computer

    To restart your computer
    1. On the Start menu, click Shut Down.
    2. Select Restart from the drop-down list and click OK.

    Take steps to prevent re-infection

    Do not reconnect your computer to the Internet until the computer is protected from re-infection. See the "Preventing Infection" section for more information.

    Transmission Methods

    MethodDescription
    Exploits VulnerabilityExploits the Windows Plug-and-Play vulnerability (MS05-039).

    Payload Information

    Payload typeTriggerDescription
    Creates files
    Execution
    Copies itself to <system folder>\mousebm.exe.
    Compromises Security
    Execution
    Connects to an IRC server to receive commands from attackers.

    Modified Registry Entries

    Added registry entries
    KeyHKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MouseBM
    Value name
    Changed registry entries
    KeyHKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLE
    Value nameEnableDCOM [String]
    Old value
    New valueN [String]
    KeyHKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
    Value namerestrictanonymous [DWORD]
    Old value
    New value1 [DWORD]

    Changed Processes

    Modified processesexplorer.exe

    Changed Services

    Added servicesmousebm.exe

    Affected Ports

    ProtocolPort number
    TCP445

    Dropped Files

    Path<system folder>\mousebm.exe


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