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Malicious Software Encyclopedia: Worm:Win32/Zotob.A

Published: September 13, 2005

Worm:Win32/Zotob.A is a network worm that exploits the Plug-and-Play vulnerability fixed in Microsoft Security Bulletin MS05-039. The worm targets computers running Microsoft Windows 2000 that do not have MS05-039 installed. The worm can also infect computers running other versions of Windows operating systems if it is delivered through e-mail, instant messaging, or other routes.

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Removal Tools - Microsoft

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
Affected PortsAffected Ports
Dropped FilesDropped Files

Threat Overview

Class/typeWorm - Network
Trojan - Backdoor
DiscoveredOctober 7, 2008
CirculatingYes
Affected operating systemsWindows 2000
Affected software Not specified
Infection ratingLow
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/Zotob.A!Worm
  • F-secure: Zotob.A
  • Global Hauri: Worm.Win32.Mytob.FR
  • Kaspersky: Net-Worm.Win32.Mytob.cd
  • McAfee: W32/Zotob.worm
  • Panda: W32/Bozor.A.worm
  • Sophos: W32/Zotob-A
  • Symantec: W32.Zotob.A
  • Trend Micro: Zotob.A

    • 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

    Worm:Win32/Zotob.A takes the following actions:
    • Creates mutex B-O-T-Z-O-R. If this mutex already exists, an error occurs and Win32/Zotob.A exits.
    • Modifies the Windows system hosts file, %windir%\system32\drivers\etc\hosts, to block access to certain antivirus and shopping Web sites.
    • Copies itself to <system folder>\botzor.exe.
    • Makes the following registry key changes. These changes cause the worm to run each time Windows starts.
      • Adds value: WINDOWS SYSTEM
        with data: botzor.exe
        in registry key: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
      • Adds value: WINDOWS SYSTEM
        with data: botzor.exe
        in registry key: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices
    • Sets data to: 4
      in value:  Start
      of registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess
      This disables the Internet Connection Firewall/Internet Connection Sharing service.
    • Creates a thread that monitors FTP connections on port 33333
    • Creates 300 threads that scan randomly generated IP addresses on port 445. If a thread connects to a computer over port 445, the thread sends exploit code to the computer. If the computer is running Windows 2000 and does not have MS05-039 installed, the exploit code connects to the attacking computer on port 8888. The attacking computer then sends a command that causes the exploited computer to download a copy of the worm using FTP. The worm then runs on the exploited computer.
    • Sends a message to an IRC server whenever a computer is successfully infected. This message includes the IP address of the exploited computer.
    • Connects to an IRC server to receive commands, which can include:
      • Updating itself using ftp.
      • Retrieving system information such as CPU speed, memory usage, Windows operating system,  connection type, IP address, and Windows logon information.
      • Downloading and running files using http.
      • Removing the worm.

    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.

    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 Worm:Win32/Zotob.A. However, your computer may be infected with Worm:Win32/Zotob.A if you notice any of the following symptoms:
    • Presence of <system folder>/botzor.exe
    • Presence of value: WINDOWS SYSTEM
      with data: botzor.exe
      in the following registry keys:
      HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
      HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices
    • Excessive network traffic over port 445

    How to Recover from Infection

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

    Manual Recovery

    To manually recover from infection by Worm:Win32/Zotob.A, follow these steps:
    1. Install security update MS05-039.
    2. Disconnect from the Internet.
    3. End the worm process.
    4. Delete the worm files from your computer.
    5. Delete the worm registry entries.
    6. Clean the system host file.
    7. Restart your computer.
    8. Take steps to prevent re-infection.

    Install 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.

    End the worm process

    Ending the worm process will help stop your computer from infecting other computers as well as resolve the crashing, rebooting, and performance degradation issues caused by the worm.
    To end the worm process
    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. Select the process botzor.exe, and click End Process.

    Delete the worm files from your computer

    To delete the worm files from your computer
    1. Click Start, and click Run.
    2. In the Open field, type the name of the system folder, for example, C:\Winnt\system32\
    3. Click OK.
    4. Click Name to sort files by name.
    5. If botzor.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 files fails, follow these steps to verify that botzor.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 botzor.exe is not in the list.

    Delete the worm registry entries

    Worm:Win32/Zotob.A creates entries in the Windows registry that attempt to run the worm every time your computer restarts. These entries should be deleted.
    To delete the worm registry entries
    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\Software\Microsoft\Windows\CurrentVersion\Run
      In the right pane, right-click the following value, if it exists:
      WINDOWS SYSTEM
    4. Click Delete and click Yes to delete the values.
    5. Repeate steps 3-4 for HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices.
    6. Close Registry Editor.

    Clean the system host file

    The worm makes changes to the system host file to prevent access to certain Web sites.
    To clean the system host file.
    1. On the Start menu, click Run.
    2. Type notepad.exe and click OK.
    3. On the File menu, click Open…
    4. In the File name text box, type the name of the Windows directory folder and \system32\drivers\etc\hosts, for example, C:\winnt\system32\drivers\etc\hosts.
    5. Search for text that begins with "Botzor2005 Made By…"
    6. Select this text and all text that follows. Delete the selected text and save the file.
    7. Close Notepad.

    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 Plug-and-Play vulnerability fixed in Microsoft Security Bulletin MS05-039.

    Payload Information

    Payload typeTriggerDescription
    Creates files
    Copies itself to <system folder>\botzor.exe.

    Modified Registry Entries

    Changed registry entries
    KeyHKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    Value nameWINDOWS SYSTEM [String]
    Old value
    New valuebotzor.exe [String]
    KeyHKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices
    Value nameWINDOWS SYSTEM [String]
    Old value
    New valuebotzor.exe [String]

    Affected Ports

    ProtocolPort number
    TCP8888
    TCP8080
    TCP445
    TCP33333

    Dropped Files

    Path<system folder>\botzor.exe
    SHA1 hashfb9033f7a974d34ec1875f91e0707b7898171d70

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