Trojan.Niska

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Discovered: April 18, 2004
Updated: February 13, 2007 12:21:32 PM
Type: Trojan Horse
Systems Affected: Windows


Trojan.Niska is a Trojan horse that deletes, and then replaces the Hosts file. It tries to download and execute a file from a Web site.

Antivirus Protection Dates

  • Initial Rapid Release version April 18, 2004
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version April 18, 2004
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date April 21, 2004

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

Writeup By: Fergal Ladley

Discovered: April 18, 2004
Updated: February 13, 2007 12:21:32 PM
Type: Trojan Horse
Systems Affected: Windows


When Trojan.Niska runs, it does the following:

  1. Deletes one of the following files:
    • Hosts.sam (if running on Windows 95, Windows 98, or Windows Me)
    • %System%\drivers\etc\hosts (if running on Windows 2000 or Windows XP)


      Note: %System% is a variable. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

  2. Replaces the Hosts file that it deleted with a file of the same name. The new Host file contains the following lines:

    65.77.83.222 thehun.com
    65.77.83.222 thehun.net
    65.77.83.222 madthumbs.com
    65.77.83.222 worldsex.com
    65.77.83.222 teeniefiles.com
    65.77.83.222 al4a.com
    65.77.83.222 sublimedirectory.com
    65.77.83.222 thumbzilla.com
    65.77.83.222 sexocean.com
    65.77.83.222 easypic.com
    65.77.83.222 absolut-series.com
    65.77.83.222 jpeg4free.com
    65.77.83.222 thumbnailpost.com

  3. Attempts to download the file, teens3.com/dialer/pipiska/in.html, save it as %System%\Mmy_teens.exe, and then run it. This file was unavailable at the time of this writing.


Recommendations

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: Fergal Ladley

Discovered: April 18, 2004
Updated: February 13, 2007 12:21:32 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.

  1. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Run a full system scan and delete all the files detected as Trojan.Niska.
  4. Edit the Hosts file.

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

1. To disable 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:

Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder ," Article ID: Q263455.

2. To update 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. To scan for and delete 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 Trojan.Niska, click Delete.


    Note: If your Symantec antivirus product reports that it cannot delete an infected file, Windows may be using the file. To fix this, run the scan in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode." Once you have restarted in Safe mode, run the scan again.

    When all the infected files have been deleted, restart the computer in Normal mode.

4. To edit the Hosts file
Follow the instructions for your operating system:
  • Windows 95/98/Me2000
    1. Click Start, point to Find or Search, and then click Files or Folders.
    2. Make sure that "Look in" is set to (C:) and that "Include subfolders" is checked.
    3. In the "Named" or "Search for..." box, type:

      hosts

    4. Click Find Now or Search Now.
    5. For each Hosts or Hosts.sam file that you find, right-click the file, and then click "Open With."
    6. Deselect the "Always use this program to open this program" check box.
    7. Scroll through the list of programs and double-click Notepad.
    8. When the file opens, see if the file contains the text shown in step 2 of the "Technical Details" section. If it does, delete all the entries in the Hosts file. Then type the following line:

      127.0.0.1     localhost

    9. Close Notepad and save your changes when prompted.

  • Windows XP
    1. Click Start, and then click Search.
    2. Click All files and folders.
    3. In the "All or part of the file name" box, type:

      hosts

    4. Verify that "Look in" is set to "Local Hard Drives" or to (C:).
    5. Click "More advanced options."
    6. Check "Search system folders."
    7. Check "Search subfolders."
    8. Click Search.
    9. Click Find Now or Search Now.
    10. For each Hosts file that you find, right-click the file, and then click "Open With."
    11. Deselect the "Always use this program to open this program" check box.
    12. Scroll through the list of programs and double-click Notepad.
    13. When the file opens, see if the file contains the text shown in step 2 of the "Technical Details" section. If it does, delete all the entries in the Hosts file. Then type the following line:

      127.0.0.1     localhost

    14. Close Notepad and save your changes when prompted.


Writeup By: Fergal Ladley