1. Symantec/
  2. Security Response/
  3. W32.DoS.Trinoo


Risk Level 1: Very Low

December 30, 1999
February 13, 2007 11:55:14 AM
Also Known As:
W32/Trinoo, Trinoo, TROJ_TRINOO
Trojan Horse

Trinoo's master component is the component that actually performs the attack. Master component is typically secretly installed on a hacked computer, or Zombie, on the Internet. Trinoo's master component is capable of broadcasting many UDP packets to a designated or targeted computer. The targeted computer tries to process and respond to these invalid UDP packets with "ICMP port unreachable" messages for each UDP packet. Because it has to respond to so many of them, it eventually runs out of network bandwidth, which results in a denial of service.
Trinoo also has a client component that is used to control the master component. This lets the hacker control multiple master components remotely. The client can communicate with the master component by sending various commands.
W32.DoS.Trinoo is a Windows compiled version of the Trinoo master component. Trinoo can also be compiled under UNIX platforms such as Linux.
When W32.DoS.Trinoo is executed, it is copied into the \windows\system directory as service.exe. It modifies the registry to load itself each time the computer is started. Once W32.DoS.Trinoo is in memory, it listens for a command such as mdos, mping, mdie, dos, mtimer, or msize from the Trinoo client program and performs the associated tasks.
It is important to detect the Trinoo master component because it can be installed secretly on your computer system by a hacker. Norton AntiVirus can detect the W95.DoS.Trinoo master component as well as other known DoS attack tools.


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: Motoaki Yamamura
Summary| Technical Details| Removal

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