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Discovered: January 31, 2003
Updated: February 13, 2007 11:57:38 AM
Type: Trojan Horse
Systems Affected: Windows

Backdoor.Krei is a backdoor Trojan that uses Trojan.Slanret to hide its malicious activities. Backdoor.Krei opens a listening port (port 449 by default) on the infected computer and it gives a hacker full access to the infected system.

Symantec Security Response has received unconfirmed reports that both Backdoor.Krei and Trojan.Slanret have been placed on systems by hackers who used a known SQL server exploit. This is the same exploit used by W32.SQLExp.Worm .

Therefore, Symantec Security Response strongly suggests that administrators patch their SQL servers.

If Backdoor.Krei was successfully installed on the computer, an unauthorized user may have remotely accessed your system. For this reason, it is impossible to guarantee the integrity of a system that has had such an infection. The hacker could have made changes to the system, including but not limited to the following:

  • Stealing or changing passwords or password files.
  • Installing remote connectivity host software, also known as backdoors.
  • Installing keystroke logging software.
  • Configuring firewall rules.
  • Stealing credit card numbers, banking information, personal data, and so on.
  • Deleting or modifying files.
  • Sending inappropriate or even incriminating material from a customer's email account.
  • Modifying access rights on user accounts or files.
  • Deleting information from log files to hide such activities.

To be certain that your organization is secure, re-install the operating system, restore files from a backup made before the infection took place, and change all the passwords that may have been on the infected computers, or that were accessible from it. This is the only way to ensure that your systems are safe. For more information regarding security in your organization, contact your system administrator.

Antivirus Protection Dates

  • Initial Rapid Release version February 03, 2003
  • Latest Rapid Release version August 20, 2008 revision 017
  • Initial Daily Certified version February 03, 2003
  • Latest Daily Certified version August 20, 2008 revision 016
  • Initial Weekly Certified release date February 05, 2003

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

Writeup By: Neal Hindocha

Discovered: January 31, 2003
Updated: February 13, 2007 11:57:38 AM
Type: Trojan Horse
Systems Affected: Windows

Backdoor.Krei is a multi-threaded application. It uses the file name Ipsechlp.dll.

When Backdoor.Krei is executed, it:

  • Immediately creates a secondary thread. The secondary thread uses Trojan.Slanret to create the service "IPSEC Helper Service."
  • Listens on port 449 for incoming commands.

Due to the use of Trojan.Slanret , all the activities that this Trojan performs may not be visible. This includes the files, registry keys, and processes. Once Trojan.Slanret has been disabled, the files, processes, and registry keys created by Backdoor.Krei will become visible again.


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: Neal Hindocha

Discovered: January 31, 2003
Updated: February 13, 2007 11:57:38 AM
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.

  1. Update the virus definitions.
  2. Run a full system scan and delete all the files detected as Backdoor.Krei or Trojan.Slanret

For specific details on each of these procedures, read the following instructions.

1. 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 the 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), in the "Protection" section, at the top of this writeup.
  • 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), in the "Protection" section, at the top of this writeup.

    The 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. 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.Krei or Trojan.Slanret, click Delete.

Writeup By: Neal Hindocha