Microsoft security software detects and removes this threat.
Worm:Win32/Esbot is a family of network worms that targets Microsoft Windows 2000 computers by exploiting the Windows Plug-and-Play buffer overflow vulnerability that is fixed with Microsoft Security Bulletin MS05-039. The worm can also infect computers running other Windows operating systems if it is delivered through e-mail, instant messaging, or other routes. The worm has a backdoor component that connects to an IRC server to receive commands from attackers.

What to do now

Use the following free Microsoft software to detect and remove this threat:

You should also run a full scan. A full scan might find hidden malware.

Get more help

You can also visit our advanced troubleshooting page or search the Microsoft virus and malware community for more help.

If you’re using Windows XP, see our Windows XP end of support page.

Threat behavior

Win32/Esbot takes the following actions:
  • Copies itself as a new file to the Windows system folder. 
  • Uses the Service Control Manager to register itself as a service that has a misleading display name.
  • Starts the worm service, if possible. If the service starts, the original worm process exits after starting a new explorer.exe process to delete the original worm file. In this case, the service performs the operations that follow. If the service does not start, the original worm process performs the operations. 
  • Checks for the presence of a particular mutex. If the mutex exists, the service or original worm process exits so that multiple instances of the worm are not running concurrently on the same computer. If the mutex does not exist, the service or original worm process takes the following actions:
    • Creates a mutex to prevent multiple instances of the worm from running on the same computer.
    • Places data in the EnableDCOM value of registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLE
    • Places data in the restrictanonymous value of registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
    • Injects its code into the explorer.exe process space and runs the injected code.
    • Scans random IP addresses to exploit the Windows Plug-and-Play vulnerability described in Microsoft Security Bulletin MS05-039. The worm may begin scanning with a random address or an address based on the IP address of the infected computer; it then scans IP addresses consecutively.
    • Connects to a specific IRC server and channel to enable attackers to perform functions such as the following:
      • Download files.  
      • Run commands or executable files.
      • Collect information such as system information and file data.


Win32/Esbot symptoms differ according to the variant. There may be no readily apparent indications that your computer is infected.


Alerts from your security software might be the only symptom.

Alert level: Severe
This entry was first published on: Aug 19, 2005
This entry was updated on: Jul 16, 2015

This threat is also detected as:
  • W32/IRCbot.gen (McAfee)
  • Esbot (Symantec)
  • BKDR_RBOT (Trend Micro)
  • W32/Backdoor.EUR (F-secure)
  • Esbot (Sophos)
  • Win32.Esbot (CA)