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Discovered: August 04, 2003
Updated: February 13, 2007 12:04:25 PM
Type: Trojan Horse
Systems Affected: Windows

Backdoor.IRC.Flood.F is a Backdoor Trojan Horse that will attempt to connect to an IRC server on port 6667. Once the Trojan is connected to the IRC server, it waits for commands from its creator.

Antivirus Protection Dates

  • Initial Rapid Release version August 05, 2003
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version August 05, 2003
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date August 06, 2003

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

Writeup By: Douglas Knowles

Discovered: August 04, 2003
Updated: February 13, 2007 12:04:25 PM
Type: Trojan Horse
Systems Affected: Windows

When Backdoor.IRC.Flood.F is executed, it does the following:

  1. Creates the following files in the C:\Winnt\Inf folder:
    • Conn.txt: This file is not viral itself, and Norton AntiVirus will not detect it.
    • Explore.dat: This file is not viral itself, and Norton AntiVirus will not detect it.
    • Network.dll: This file is a list of user names and is not viral.
    • Nite.exe: This file is a Denial of Service (DoS) Tool, and Norton AntiVirus will detect it as Hacktool.DoS.
    • Os32.dll: This is an IRC script.
    • Vlxd.bat: This is a batch file that will attempt to launch the IRC client over network shares.
    • Vlxd.exe: This is a dropper of all of the rootkit package.
    • Vlxd.cfg: This is a configuration file, and Norton Antivirus will not detect this file.
    • Winx.dll: This an IRC script that is not detected.
    • Psexec.exe: This file is not viral itself, and Norton AntiVirus will not detect it.
    • Pnp11.exe: This file is not viral itself, and Norton AntiVirus will not detect it.
    • Smss.exe: This is an IRC client that will connect to a server on port 6667.

  2. Adds the value:

    "SMSS" = "C:\Winnt\system32\CatRoot\smss.exe"

    to the registry key:


    so that the Trojan runs when you start Windows.

  3. Attempts to connect to an IRC server on port 6667. Once connected, it will await commands from the Trojan's creator.

  4. Attempts to remotely launch Vlxd.exe using network shares. The process is launched by using Psexec.exe.

    Note: Psexec.exe is a legitimate tool called PsExec from sysinternals, and therefore Norton AntiVirus will not detect the process.
  5. Before the process is launched, the Vlxd.exe file will be copied to the remote computer.

  6. Attempts to gain access on the remote machine by using the user names "Administrator," "Admin," "root," "Owner," "User," and "Student" with many different passwords, some of which are:
    • [Blank]
    • pass123
    • something
    • mypass
    • login
    • access
    • password
    • matrix
    • security
    • success
    • special
    • ultra
    • pass


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: Douglas Knowles

Discovered: August 04, 2003
Updated: February 13, 2007 12:04:25 PM
Type: Trojan Horse
Systems Affected: Windows

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

Note: Symantec recommends removing the system from the network prior to removing this threat. Otherwise, it may get re-infected.
  1. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Delete the value that was added to the registry and reboot the system.
  4. Run a full system scan and delete all the files detected as Backdoor.IRC.Flood.F.
  5. If required, delete the additional files that Backdoor.IRC.Flood.F created.
For specific details on each of these steps, read the following instructions.

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:
For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Anti-Virus Tools Cannot Clean Infected Files in the _Restore Folder ," Article ID: Q263455.

2. Updating 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.

3. Deleting the value from the registry

CAUTION: 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

    Then click OK. (The Registry Editor opens.)

  3. Navigate to the key:


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

  5. Exit the Registry Editor.

4. 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.IRC.Flood.F, click Delete.

5. Removing the additional files
  1. Using Windows Explorer, browse to the folder, C:\Winnt\System32\CatRoot\MSA.
  2. Find and delete the following files:
    • Conn.txt
    • Psexec.exe
    • Winx.dll
    • Pnp11.exe
    • Vlxd.cfg
    • Explore.dat
    • Network.dll

Writeup By: Douglas Knowles