Discovered: September 30, 2003
Updated: February 13, 2007 12:13:04 PM
Also Known As: W32/Gaobot.worm.gen.b [McAfee], Backdoor.Agobot.3.x [Kaspersky
Type: Worm
Systems Affected: Windows

W32.HLLW.Gaobot.AO is a minor variant of W32.HLLW.Gaobot.AF . It attempts to spread to network shares that have weak passwords and allows hackers to access an infected computer through IRC.

The worm uses multiple vulnerabilities to spread, including:

W32.HLLW.Gaobot.AO is compressed with UPX.

Note: Virus definitions dated prior to October 1, 2003 may detect this worm as a hack tool.

Note: Virus definitions dated November 19, 2003 and later contain a modified W32.HLLW.Gaobot.AO signature to account for the discovery of a minor variant.

Antivirus Protection Dates

  • Initial Rapid Release version October 01, 2003
  • Latest Rapid Release version August 08, 2016 revision 023
  • Initial Daily Certified version October 01, 2003
  • Latest Daily Certified version August 09, 2016 revision 001
  • Initial Weekly Certified release date October 01, 2003

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Heather Shannon

Discovered: September 30, 2003
Updated: February 13, 2007 12:13:04 PM
Also Known As: W32/Gaobot.worm.gen.b [McAfee], Backdoor.Agobot.3.x [Kaspersky
Type: Worm
Systems Affected: Windows

When W32.HLLW.Gaobot.AO runs, it does the following:

  1. Copies itself into the %System% folder as one of the following:
    • Cavapsvc.exe
    • Csrrs.exe
    • Cvhost.exe
    • DIIhost.exe (with capital letter 'i')
    • Dosrun32.exe
    • Dos32.exe
    • Lsas.exe
    • Regloadr.exe
    • Schost.exe
    • Scvhost.exe
    • Service.exe
    • Servicess.exe
    • Sochost.exe
    • Swchost.exe
    • System.exe
    • Update.exe
    • Wdrun32.exe
    • Winhlpp32.exe
    • Winreg.exe
    • Winupdsdgm.exe

      Note: %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

  2. Adds one of the following values:
    • "Registry Loader"="regloadr.exe"
    • "Registry Loader"="winhlpp32.exe"
    • "Update Installer" = "Swchost.exe"
    • "Windows Explorer" = "Lsas.exe"
    • "Configuration Loader" = "dosrun32.exe"
    • "Configuration Loader" = "Service.exe"
    • "Configuration Loader" = "Winreg.exe"
    • "Configuration Loader" = "System.exe"
    • "Automatic Windows Updater" = "Update.exe"
    • "Microsoft Windows 2000" = "Winupdsdgm.exe"
    • "Window Loader" = "Dos32.exe"
    • "iConfigLoader" = "DIIhost.exe"
    • "Config Loader" = "Scvhost.exe"
    • "Update Install" ="Schost.exe"
    • "Startup Update" = "Cvshost.exe"
    • "Norton Live Updater" = "Cavapsvc.exe"
    • "Service Controller" = "Csrrs.exe"
    • "Configuration Loader" = "Servicess.exe"
    • "Windows Startup" = "Wdrun32.exe"
    • "Norton Live Updater" = "Sochost.exe"

      to these registry keys:
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices

      so that the worm starts when Windows starts.

  3. Adds the following registry keys :
    • HKEY_LOCAL_MACHINE\System\CurrentControlSet\enum\root\LEGACY_A3X
    • HKEY_LOCAL_MACHINE\System\CurrentControlSet\services\A3X
    • HKEY_LOCAL_MACHINE\System\ControlSet001\enum\root\LEGACY_A3X
    • HKEY_LOCAL_MACHINE\System\ControlSet001\services\A3X
    • HKEY_LOCAL_MACHINE\System\ControlSet002\enum\root\LEGACY_A3X
    • HKEY_LOCAL_MACHINE\System\ControlSet002\services\A3X

  4. Opens a randomly selected TCP port to connect to a hacker.

  5. Connects to a predefined IRC channel, using its own IRC client, and listens for the commands from a hacker.

  6. Allows a hacker to remotely control a compromised computer, which allows him/her to perform any of the following actions:
    • Manage the installation of the worm
    • Dynamically update the installed worm
    • Download and execute files
    • Steal system information
    • Send the worm to other IRC users
    • Add new accounts

  7. Sends data to TCP ports135 and 445, which exploits the DCOM RPC vulnerability.

  8. Probes the following shares:
    • admin$
  • c$
  • d$
  • e$
  • print$

    using the following user names and passwords, as well as any user names found using NetUserEnum():

  • Admin
    • Administrador
    • Administrateur
    • Administrator
    • Default
    • Dell
    • Gast
    • Guest
    • Inviter
    • Owner
    • Standard
    • Test
    • User
    • a
    • aaa
    • abc
    • admin
    • administrator
    • asdf
    • home
    • mgmt
    • pc
    • qwer
    • temp
    • test
    • win
    • x
    • xyz

    • 0
    • 007
    • 000000
    • 00000000
    • 1
    • 110
    • 111
    • 111111
    • 11111111
    • 12
    • 121212
    • 123
    • 123123
    • 1234
    • 12345
    • 123456
    • 1234567
    • 12345678
    • 123456789
    • 1234qwer
    • 123abc
    • 123asd
    • 123qwe
    • 2002
    • 2600
    • 54321
    • 654321
    • 88888888
    • Internet
    • Login
    • Password
    • a
    • aaa
    • abc
    • abcd
    • alpha
    • computer
    • database
    • enable
    • foobar
    • god
    • godblessyou
    • home
    • ihavenopass
    • login
    • love
    • mypass
    • mypc
    • oracle
    • owner
    • pass
    • passwd
    • password
    • pat
    • patrick
    • pc
    • pw
    • pwd
    • root
    • secret
    • server
    • sex
    • super
    • sybase
    • temp
    • test
    • win
    • xp
    • xxx
    • yxcv
    • zxcv

8. Copies itself to any systems it compromised using the aforementioned exploits.

9. Steals the CD keys of various games, including:
    • Soldier of Fortune II - Double Helix
    • Neverwinter
    • Westwood\Nox
    • Tiberian Sun
    • Red Alert 2
    • Red Alert
    • Project IGI 2
    • Command & Conquer Generals
    • Battlefield 1942 Secret Weapons of WWII
    • Battlefield 1942 The Road to Rome
    • Battlefield 1942
    • Rainbow Six III RavenShield
    • Nascar Racing 2003
    • Nascar Racing 2002
    • NHL 2003
    • NHL 2002
    • FIFA 2003
    • FIFA 2002
    • Need For Speed Hot Pursuit 2
    • The Gladiators
    • Unreal Tournament 2003
    • Legends of Might and Magic
    • Counter-Strike
    • Half-Life

10. Ends numerous processes that are associated with antivirus and firewall software, including:
    • ACKWIN32.EXE
    • AVE32.EXE
    • AVNT.EXE
    • AVP.EXE
    • AVP32.EXE
    • AVPDOS32.EXE
    • AVPM.EXE
    • AVPTC32.EXE
    • AVWIN95.EXE
    • AVWUPD32.EXE
    • CFINET32.EXE
    • CLAW95.EXE
    • CLAW95CF.EXE
    • DVP95.EXE
    • DVP95_0.EXE
    • F-AGNT95.EXE
    • F-PROT.EXE
    • F-PROT95.EXE
    • FP-WIN.EXE
    • FRW.EXE
    • ICLOAD95.EXE
    • ICSUPP95.EXE
    • IOMON98.EXE
    • JEDI.EXE
    • LOCKDOWN2000.EXE
    • N32SCANW.EXE
    • NAVAPW32.EXE
    • NAVLU32.EXE
    • NAVW32.EXE
    • NVC95.EXE
    • PAVW.EXE
    • PCCWIN98.EXE
    • RAV7.EXE
    • SCAN32.EXE
    • SCAN95.EXE
    • SERV95.EXE
    • SMC.EXE
    • SWEEP95.EXE
    • TCA.EXE
    • TDS2-98.EXE
    • TDS2-NT.EXE
    • VET95.EXE
    • VSCAN40.EXE
    • VSHWIN32.EXE
    • WFINDV32.EXE
    • _AVP32.EXE
    • _AVPCC.EXE
    • _AVPM.EXE

11. Attempts to kill some processes associated with other worms, including:
    • dllhost.exe
    • msblast.exe
    • mspatch.exe
    • penis32.exe
    • scvhosl.exe
    • tftpd.exe
    • winppr32.exe


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: Heather Shannon

Discovered: September 30, 2003
Updated: February 13, 2007 12:13:04 PM
Also Known As: W32/Gaobot.worm.gen.b [McAfee], Backdoor.Agobot.3.x [Kaspersky
Type: Worm
Systems Affected: Windows

Removal using the Removal Tool
Symantec Security Response has developed a removal tool to clean the infections of W32.HLLW.Gaobot.AO. This is the preferred method in most cases.

Manual Removal
Perform a manual removal if you cannot obtain the tool.

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Do one of the following:
    • Windows 95/98/Me: Restart the computer in Safe mode.
    • Windows NT/2000/XP: End the Trojan process.
  4. Run a full system scan and delete all the files detected as W32.HLLW.Gaobot.AO, or similar variants.
  5. Reverse the changes that the Trojan made to the registry.
For details on each of these steps, read the following instructions.

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:
Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

  • Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).

    Note: If the worm is running, it attempts to end the LiveUpdate process. It is not always successful in doing so. If you find that LiveUpdate does not work, download the definitions using the Intelligent Updater as described in the next paragraph.

  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. Restarting the computer in Safe mode or ending the Trojan process
    Windows 95/98/Me
    Restart the computer in Safe mode. All the Windows 32-bit operating systems, except for Windows NT, can be restarted in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."

    Windows NT/2000/XP
    To end the Trojan process:
    1. Press Ctrl+Alt+Delete once.
    2. Click Task Manager.
    3. Click the Processes tab.
    4. Double-click the Image Name column header to alphabetically sort the processes.
    5. Scroll through the list and look for any of the file names mentioned in step 1 of the "Technical Details" section.
    6. If you find the file, click it to highlight it, and then click End Process.
    7. Exit the Task Manager.
4. Scanning for and deleting the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as W32.HLLW.Gaobot.AO, write down the path and file names, and then click Delete.

5. Reversing the changes made to the registry

WARNING: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry ," for instructions.

  1. Click Start, and then click Run. (The Run dialog box appears.)
  2. Type regedit

    and then click OK. (The Registry Editor opens.)

  3. Navigate to each of the keys:
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\

      Note: The RunServices key is not usually found on Windows NT/2000/XP systems.

  4. In the right pane, delete any values that refer to the files that were detected as the worm.
    For example:
    • "Registry Loader"="regloadr.exe"
    • "Registry Loader"="winhlpp32.exe"
    • "Update Installer" = "Swchost.exe"
    • "Windows Explorer" = "Lsas.exe"
    • "Configuration Loader" = "dosrun32.exe"
    • "Configuration Loader" = "Service.exe"
    • "Configuration Loader" = "Winreg.exe"
    • "Configuration Loader" = "System.exe"
    • "Automatic Windows Updater" = "Update.exe"
    • "Microsoft Windows 2000" = "Winupdsdgm.exe"
    • "Window Loader" = "Dos32.exe"
    • "iConfigLoader" = "DIIhost.exe"
    • "Config Loader" = "Scvhost.exe"
    • "Update Install" ="Schost.exe"
    • "Startup Update" = "Cvshost.exe"
    • "Norton Live Updater" = "Cavapsvc.exe"
    • "Service Controller" = "Csrrs.exe"
    • "Configuration Loader" = "Servicess.exe"
    • "Windows Startup" = "Wdrun32.exe"
    • "Norton Live Updater" = "Sochost.exe"

  5. Navigate to each of the keys:


  6. In the left pane, delete the subkey: A3X

    from each of the subkeys listed above.

  7. Exit the Registry Editor.

Writeup By: Heather Shannon