1. Symantec/
  2. Security Response/
  3. W32.Toal.A@mm


Risk Level 2: Low

October 23, 2001
February 13, 2007 11:37:30 AM
Also Known As:
Worm, Virus

When the worm is executed, it queries a mutex to see whether another copy of itself is running. If another copy is already running, the worm exits. Otherwise, it creates a mutex and then creates the following files:
  • %System%\Invictus.dll. This file is used to infect executable files on the system.
  • %Windows%\<3 random characters>.exe. The Hidden attribute of this file is turned on, and the file is executed immediately after being created. This file is run-time compressed, and it orchestrates the entire worm execution flow by performing some actions itself and by calling functions in Invictus.dll.

  • %Windows% is a variable. The worm locates the Windows folder (by default this is C:\Windows or C:\Winnt) and creates the file in that location.
  • %System% is a variable. The worm locates the Windows System folder (by default this is C:\Windows\System or C:\Winnt\System32) and creates the file in that location.

Next, the worm modifies the System.ini file. The line


is changed to

shell=Explorer.exe [3 random characters].exe

This causes the worm to run the next time that you restart the computer.

The worm then searches for files to infect by using undocumented TaskMan API functions. Infections may be both polymorphic and entry-point obscuring. The worm specifically infects Hh.exe, which is a standard Windows executable file.

The worm also enumerates Network Neighborhood to infect remote machines. The worm copies itself as a random three-letter name with the .exe extension to the remote Windows directory and Invictus.dll to the remote Windows System directory. To execute itself on the remote system, the worm modifies the remote System.ini file, as mentioned previously.

The worm gathers email addresses by searching the ICQ White Pages, which reside on an ICQ Web server. To send itself, the worm uses an educated guess at what is an appropriate email server. For example, if the email address is joeuser@domain.tld, the worm will use the email servers smtp.domain.tld or mail.domain.tld. When it sends the email message, the worm attaches the infected Hh.exe file as Binladen_brasil.exe. The worm does not require a particular email client to propagate.

The message body is blank and the subject will vary. The subject lines are all references to the current situation in Afghanistan and may be in different languages. The language of the subject line is chosen based on the language version of the operating system.

The worm attempts to save cached networking passwords to a local file using an undocumented Windows 95 function. This fails on other versions of Windows.

The worm creates a share on the local drive C drive. It shares drive C by modifying the registry key


The worm also attempts to disable antivirus software in memory.

Depending on the length of time that has passed since it was first executed, the worm may display messages using randomly changing background and text colors that refer to the current activity in Afghanistan. Then a message box is displayed, and random rectangles on the screen are interchanged.

Finally, the worm sleeps for five minutes and repeats the infection process.

Norton AntiVirus already detects Invictus.dll as W32.Invictus.dll. This file is crucial to the propagation of the worm, and the worm may not function properly without it.


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: Andre Post
Summary| Technical Details| Removal

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