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Discovered: October 09, 2001
Updated: February 13, 2007 11:37:25 AM
Type: Trojan Horse

Backdoor.Slackbot.B is a backdoor Trojan horse that allows a hacker to control your computer using Internet Relay Chat (IRC). Backdoor.Slackbot.B can update itself by checking for newer versions over the Internet.

Possible system changes
If the Trojan has been executed and a hacker has executed files on your computer, it may be difficult to determine exactly what has been done, even after the Trojan has been removed. If you are familiar with your operating system and how to use system repair or system checking tools, we suggest that you fully check the system for any of these modifications and revert them. Otherwise, consider reinstalling the operating system.

What are Portable Executable (PE) files?
PE files are files that are portable across all Microsoft 32-bit operating systems. The same PE-format executable can be executed on any version of Windows 95, 98, Me, NT, and 2000. Therefore, all PE files are executable, but not all executable files are portable.

A good example of a Portable Executable is a screen saver (.scr) file.

Antivirus Protection Dates

  • Initial Rapid Release version October 10, 2001
  • Latest Rapid Release version November 04, 2019 revision 019
  • Initial Daily Certified version October 10, 2001 revision 004
  • Latest Daily Certified version November 04, 2019 revision 065
  • Initial Weekly Certified release date October 10, 2001

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

Technical Description

Backdoor.Slackbot was created using a special tool; it arrives in the form of a Portable Executable (PE) file. When it is run, it creates a copy of itself as the file \%Windows%\Zwbv.exe.

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

It also adds the value data


to the registry key


so that the Trojan is run each time that you start Windows.

This backdoor Trojan contains its own Internet Relay Chat (IRC) client. This allows it to connect to an IRC channel that was coded into the Trojan by the hacker who created it. Using the IRC channel, Backdoor.Slackbot listens for commands from the hacker. The commands allow the hacker to perform any of the following actions:

  • Manage the installation of the backdoor
  • Control the IRC client on the compromised computer
  • Dynamically update the installed backdoor
  • Send the backdoor to other IRC channels to attempt to compromise more computers
  • Download and execute files


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.


To remove this Trojan, delete files detected as Backdoor.Slackbot.B and remove the value that it added to the registry.

To delete the Trojan

  1. Run LiveUpdate to make sure that you have the most recent virus definitions.
  2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
  3. Run a full system scan.
  4. Delete all files that are detected as Backdoor.Slackbot.B.

To edit the registry:

CAUTION : We strongly recommend that you back up the system registry before you make any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure that you modify only the keys that are specified. Please see the document How to back up the Windows registry before you proceed.
  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, look for a value data that refers to:

  5. Delete this value if you find it.
  6. Click Registry, and then click Exit.

Writeup By: Andre Post