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Category 1

Trinoo is not a virus, but an attack tool released in late December 1999 that performs a distributed Denial of Service attack. W32.DoS.Trinoo is a Windows compiled version of the Trinoo master component.

Also Known As: W32/Trinoo, Trinoo, TROJ_TRINOO
Type: Trojan Horse
Infection Length: 23,145 bytes

  • Virus Definitions (Intelligent Updater)
  • February 22, 2000

    threat assessment


    Threat Metrics

    Low Medium Low





    • Payload: Degrades performance:Can be used in a distributed Denial of Service attack.


    technical details

    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":

    • Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
    • If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
    • 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.
    • Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
    • Isolate infected computers quickly to prevent further compromising your organization. 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.

    removal instructions

    Using Windows Explorer delete the following file:


    Using regedit delete the following registry key:

    HKLM\Software\Microsoft\Windows\CurrentVersion\Run\"System Services"="service.exe"

    Write-up by: Motoaki Yamamura