Threat Explorer

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26 October 1999
13 February 2007
Also Known As:
RingZero.gen Trojan, Trojan.Rhino

This Trojan runs as a hidden process, and it sends and retrieves data over an Internet connection.

Antivirus Protection Dates

  • Initial Rapid Release version 26 October 1999
  • Latest Rapid Release version 07 May 2019 revision 006
  • Initial Daily Certified version 26 October 1999
  • Latest Daily Certified version 07 May 2019 revision 008
  • Initial Weekly Certified release date pending
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

There are three versions of the Trojan horse:
  • Its.exe
    Its.exe copies itself to the \Windows\System folder when executed for the first time. It also drops the Ring0.vxd file into the same folder. Its.exe is executed again the next time that Windows starts. At this time, it creates another file to hold its data, Its.dat. It then tries to connect to two Web sites that contain strings that attempt to send mail to an address at a pager service using the Microsoft mail server.
  • Pst.exe
    Pst.exe installs itself in the same manner as Its.exe, and also drops the Ring0.vxd file into the same folder. It attempts to connect to a different Web site than those that Its.exe tries to access.
  • Telnet23.exe
    Telnet23.exe is another version that appears to steal Windows cached passwords. It attempts to reach a Web site and send email.

These Trojans can be packed within other host programs. When you run the host program, the Trojan is installed on the computer. RingZero hides its process by registering itself as a Windows service, so it is not displayed in the Windows task manager. It also hides its entry in the Windows registry. If the Trojan is not running, the startup call in the registry \Run key is visible.


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 RingZero.Trojan, and remove references from the \Run key.

To delete the files:
  1. Run LiveUpdate to make sure that you have the most recent virus definitions.
  2. Start Norton AntiVirus (NAV), and run a full system scan, making sure that NAV is set to scan all files.
  3. Delete any files detected as RingZero.Trojan. If NAV is not able to delete the files, do the following:
    1. Write down the names and locations of the files that NAV detected.
    2. Restart the computer in MS-DOS mode, or boot to a clean DOS boot floppy disk.
    3. Delete the detected files from the \Windows\System folder.
    4. Delete the Its.dat and Ring0.dat files from the \Windows\System folder.
    5. Restart Windows.

To edit the registry:

CAUTION : We strongly recommend that you back up the system registry before making any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure you modify only the keys specified. Please see the document How to back up the Windows registry before proceeding.
  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 the following values, and if found, delete them:

    DK32 support PST "pst.exe"
    DK32 support ITS "its.exe"
    Description of EPS II "telnet23.exe"

Writeup By: Wason Han