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Updated: February 13, 2007 11:59:22 AM
Type: Trojan Horse

Backdoor.Rat.Client is a client program which allows access to Backdoor.Rat.

When Backdoor.Rat is installed on a Microsoft Windows system, this backdoor Trojan horse program lets others gain full access to the system through a network connection. Backdoor.Rat is divided into 2 parts: a client and a server. Both applications are capable of running under Windows 95, 98, and NT 4.0. The client application running on one computer might be used to monitor and control a second computer running the server application.

The port number through which the client controls the server is configurable. However, as long as the port is blocked by a firewall, this Trojan horse cannot infiltrate the server. It does not matter whether the TCP or UDP protocol is implemented. There have not been any reports of this program breaking through a firewall.

Antivirus Protection Dates

  • Initial Rapid Release version June 25, 2000
  • Latest Rapid Release version August 20, 2008 revision 017
  • Initial Daily Certified version June 25, 2000
  • Latest Daily Certified version August 20, 2008 revision 016

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

Technical Description

Backdoor.Rat is a Trojan Horse program that is divided into 2 parts: a client and a server. The client is used to connect to the server by the Internet or a LAN with TCP/IP. The server might be configured with several different options. The networking protocol could be TCP or UDP. Any port number between 1 and 65535 could be selected for communication.

To connect to the server, it must be running on the computer to which you want to connect. The IP (Internet Protocol) address of the target computer is also needed. The server masks itself as install.exe when sent to a target computer. Once the file is executed, it installs itself and is launched every time Windows starts up. The server program will not be listed in the task list (Ctrl+Alt+Del).

The client interface is used to operate the server. The following is a list of commands that the client might be sending to the server:

  • Lock/unlock mouse pointer.
  • Hide the Taskbar and disable the Start button.
  • Set the volume control.
  • Disable all Windows key combinations such as Ctrl+Alt+Del, Alt+Tab, and Ctrl+Esc.
  • Choose up to a total of 7 ASCII drawing characters to print on the server printer, which will appear as pictures, such as a big head of an alien, a devil, or the Simpson's family.
  • Log all pressed keys and all shell actions.
  • Show all passwords, active processes, and port connections.
  • Disconnect ICQ, mIRC, and all Internet services.
  • Copy, delete, rename, upload, and download files or directories.
  • Create, set, or delete registry keys.


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.


Removal of Backdoor.Rat.Client is done simply by deleting the file detected as Backdoor.Rat.Client.

Writeup By: Douglas Knowles