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Discovered: August 30, 2002
Updated: February 13, 2007 11:51:09 AM
Also Known As: Backdoor.Antilam.20.b [Kaspers, BackDoor-AJW [McAfee], Troj/Antilam [Sophos]
Type: Trojan Horse
Systems Affected: Windows

Backdoor.AntiLam.20 is a Backdoor Trojan horse that gives an attacker unauthorized access to an infected computer. Backdoor.AntiLam.20 is a Delphi application and is packed with UPX v1.05-1.22.

The Backdoor Trojan will listen for connections on TCP ports 29999 and 47891.

Antivirus Protection Dates

  • Initial Rapid Release version August 30, 2002
  • Latest Rapid Release version August 08, 2016 revision 023
  • Initial Daily Certified version August 30, 2002 revision 002
  • Latest Daily Certified version August 09, 2016 revision 001
  • Initial Weekly Certified release date September 04, 2002

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

Writeup By: Serghei Sevcenco

Discovered: August 30, 2002
Updated: February 13, 2007 11:51:09 AM
Also Known As: Backdoor.Antilam.20.b [Kaspers, BackDoor-AJW [McAfee], Troj/Antilam [Sophos]
Type: Trojan Horse
Systems Affected: Windows

Backdoor.AntiLam.20 is a variant of Backdoor.AntiLam.

When Backdoor.AntiLam.20 runs, it performs the following actions:

  1. Copies itself as %Windir%\Help.exe or %System%\Winmrg.exe.

  2. Creates the file, %windir%\Scan.dll, which has a file size of 6,144 bytes. Norton AntiVirus detects this as PWS.Hooker.Trojan.

    %Windir% is a variable. The Trojan locates the Windows main installation folder (by default this is C:\Windows or C:\Winnt) and uses it as a destination folder.

  3. The Trojan creates the registry key:


    and then adds values to this key, which the Trojan uses for configuration.

  4. Creates the value:

    Start    ok

    in the registry key:


  5. Adds the value:

    "MS Scandisk"="%windir%\Help.exe"



    to these registry keys:


    so that the Trojan runs each time you start Windows.

The Trojan attempts to disable some antivirus and firewall programs by terminating the active processes.

If the operating system is Windows 95/98/Me, the Trojan will register itself as a service process to continue running after you log off. In this case, Backdoor.AntiLam.20 closes only when the system is shut down.

Backdoor.AntiLam.20 relies on an officially undocumented function, WNetEnumCachedPasswords, which exists only in versions of the file Mpr.dll, which are written for Windows 95/98/Me. This Trojan uses this function to obtain an access to the password cache that is stored on the local computer. The cached passwords include modem and dial-up passwords, URL passwords, share passwords, as well as others.

The Trojan retrieves the properties of the current default phonebook file. Then, it retrieves the following connection information for the last successfully established RAS connection:
  • The phone number
  • The user's user name
  • The user's password

The Trojan uses the information to authenticate its access to the remote access server.

The Trojan installs hook procedures into a hook chain to monitor the system for any keyboard and mouse messages. The keyboard and mouse hook procedures process the messages and pass the hook information to the next hook procedure in the current hook chain. This permits Backdoor.AntiLam.20 to intercept keystrokes, as well as any text on the screen.

After Backdoor.AntiLam.20 is installed, it notifies the client side, using ICQ pager, and establishes a connection with the hacker through a password-protected authorization.

The commands allow the hacker to perform any of the following actions:
  • Deliver system and network information to the hacker, including login names and cached network passwords
  • Print text, play media files, and open or close the CD-ROM drive
  • Hide icons, the system tray, buttons, and the taskbar
  • Switch the monitor off and on
  • Intercept confidential information by hooking keystrokes and intercepting information displayed on the screen, and deliver it to the hacker
  • Manage the installation of the backdoor Trojan
  • Download and execute files
  • Alter many system parameters, such as screen resolution and system colors
  • Use a known vulnerability on Windows 95/98/Me to cause a user's system to crash


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: Serghei Sevcenco

Discovered: August 30, 2002
Updated: February 13, 2007 11:51:09 AM
Also Known As: Backdoor.Antilam.20.b [Kaspers, BackDoor-AJW [McAfee], Troj/Antilam [Sophos]
Type: Trojan Horse
Systems Affected: Windows

NOTE: These instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Update the virus definitions.
  2. Do one of the following:
    • Windows 95/98/Me: Restart the computer in Safe mode.
    • Windows NT/2000/XP: Stop the running Trojan process.
  3. Run a full system scan and delete all the files detected as Backdoor.AntiLam.20.
  4. Reverse the changes that the Trojan made to the registry.
For specific details on how to do this, read the following instructions.

1. Update 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).
  • 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.

2. Restarting the computer in Safe mode or stopping the 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 stop 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 Help.exe.
  6. If you find the file, click it, and then click End Process.
  7. Close the Task Manager.
3. 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 infected with Backdoor.AntiLam.20, click Delete.

4. Reversing the changes made to the registry

: 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, in turn, to each of these keys:


    For each key, delete any of the following values from the right pane:

    "MS Scandisk"="%windir%\Help.exe"


  4. Delete following the registry key:


  5. Navigate to the following key:


  6. In the right pane, delete the following value: Start
  7. Exit the Registry Editor.

Writeup By: Serghei Sevcenco