Printer Friendly Page

Discovered: July 15, 2002
Updated: February 13, 2007 11:39:38 AM
Also Known As: W32.Frethem.K@mm, I-Worm.Frethem.l [KAV], W32/Frethem.l@MM [McAfee], WORM_FRETHEM.K [Trend], W32/Frethem-Fam [Sophos], Win32.Frethem.K [CA], W32/Frethem.K [Panda], W32/Frethem.L [F-Prot]
Type: Worm
Systems Affected: Windows
CVE References: CVE-2001-0154

Due to a decreased rate of submissions, Symantec Security Response has downgraded the threat level of this worm from Category 3 to Category 2 as of May 5, 2003.

NOTE: Virus definitions dated prior to July 17, 2002 detect this as W32.Frethem.K@mm.

W32.Frethem.L@mm is a worm, and is a variant of W32.Frethem.B@mm . It uses its own SMTP engine to send itself to email addresses that it finds in the Microsoft Windows Address Book and in .dbx, .wab, .mbx, .eml, and .mdb files. The email message arrives with the following characteristics:

Subject: Re: Your password!
Attachments: Decrypt-password.exe and Password.txt

Removal tool
Symantec has provided a tool to remove infections of W32.Frethem@mm. Click here to obtain the tool. This is the easiest way to remove these threats and should be tried first.

Antivirus Protection Dates

  • Initial Rapid Release version July 15, 2002
  • Latest Rapid Release version August 08, 2016 revision 023
  • Initial Daily Certified version July 15, 2002
  • Latest Daily Certified version August 09, 2016 revision 001
  • Initial Weekly Certified release date July 15, 2002

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

Technical Description

When this worm is executed, it does the following:

It copies itself to the file %windir%\Taskbar.exe

NOTE: %windir% is a variable. The worm locates the Windows main installation folder (by default this is C:\Windows or C:\Winnt) and copies itself to that location.

It then configures itself to start when you start Windows by adding the value:

Task Bar     %windir%\taskbar.exe

to the registry key:


Next, the worm obtains the computer user's SMTP server, email address, and SMTP user name from the following registry entries:

Internet Account Manager\Accounts\00000001\SMTP Server

Internet Account Manager\Accounts\00000001\SMTP Email Address

Internet Account Manager\Accounts\00000001\SMTP Display Name

The worm then obtains email addresses from the Microsoft Windows Address Book and from .dbx, .wab, .mbx, .eml, and .mdb files, and sends itself to those addresses. The email message has the following characteristics:

Subject: Re: Your password!


You can access
very important
information by
 this password

password to disk
use your mind

now press


NOTE : The Decrypt-password.exe attachment is a copy of the worm. It is packed with UPX and PE-Pack, and its size is approximately 48 KB. The second attachment, Password.txt, is a text file that is approximately 93 bytes in length. Password.txt is not viral by itself as such, it is not detected by Symantec antivirus products. However, if the computer was infected by W32.Frethem.L@mm worm, you should delete the file manually.

When the worm arrives by email, it uses both an IFRAME exploit and a MIME exploit, which allow the virus to be executed when you read or even preview the file. Information and a patch for MIME exploit can be found at http://www.microsoft.com/technet/security/bulletin/MS01-020.asp .

The worm creates the "IEXPLORE_MUTEX_AABBCCDDEEFF" mutex. This mutex allows only one instance of the worm to execute in memory.

After sleeping for several hours, the worm copies itself to C:\Windows\All Users\Start Menu\Programs\Startup\Setup.exe so that it is executed each time that you start Windows.


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.


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

Removal tool
Symantec has provided a tool to remove infections of W32.Frethem@mm. Click here to obtain the tool. This is the easiest way to remove these threats and should be tried first.

Manual Removal

  1. Update the virus definitions, run a full system scan. Delete all files that are detected as W32.Frethem.L@mm.
  2. Delete the value

    Task Bar

    from the registry key


For details on how to do this, read the following instructions.

To scan for and delete the infected files:
  1. Obtain the most recent virus definitions. There are two ways to do this:
    • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
    • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.

      Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
  2. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
  3. Run a full system scan.
  4. Delete all files that are detected as W32.Frethem.L@mm.

    NOTE: If NAV reports that it cannot delete an infected file, you must shut down the computer, turn off the power, and wait 30 seconds. Then restart the computer in Safe mode and run the scan again. All Windows 32-bit operating systems except Windows NT can be restarted in Safe mode. For instructions on how to do this, read the document How to start the computer in Safe Mode.

    To remove the value from the registry:

    CAUTION : Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.
    1. Click Start, and click Run. The Run dialog box appears.
    2. Type regedit and then click OK. The Registry Editor opens.
    3. Navigate to the following key:

    4. In the right pane, delete the following value:

      Task Bar
    5. Exit the Registry Editor

    Writeup By: Douglas Knowles