The Win32/Rbot family of backdoor Trojans targets certain versions of Microsoft Windows. After the Trojan infects a computer, it allows attackers to control the computer through an IRC channel. Some commands instruct Win32/Rbot to spread to other computers by scanning for network shares with weak passwords, exploiting various Windows vulnerabilities, or spreading through backdoor ports opened by other families of malicious software. The Trojan also allows attackers to perform other backdoor functions, such as launching denial of service (DoS) attacks against certain Web sites and retrieving system information from infected computers. 

What to do now

To detect and remove this threat and other malicious software that may be installed in your computer, run a full-system scan with an up-to-date antivirus product such as the following:
For more information on antivirus software, see

Threat behavior

Note: August 15, 2005 - A new variant of Backdoor:Win32/Rbot has been discovered that adds the capability of spreading by exploiting Plug-and-Play vulnerability that is fixed in Microsoft Security Bulletin MS05-039.
Note: June 7, 2005 - A new variant of Backdoor:Win32/Rbot has been discovered that adds the capability of spreading by exploiting the Windows ASN.1 vulnerability that is fixed in Microsoft Security Bulletin MS04-007.
When Win32/Rbot runs, it copies itself to %windir% or <system folder>. In many cases, it adds a value to registry keys:
These changes cause the Trojan to run whenever Windows starts. Some variants can also add a Windows system service to attain similar results.
Win32/Rbot can spread to remote computers by trying weak passwords that it draws from a list. The Trojan may also scan for open ports and connect to a specific IRC server and join a specific channel to receive commands, such as IRC commands to exploit various Windows vulnerabilities. For example, it may exploit the MS03-026 vulnerability to create a remote shell on the target computer. The Trojan uses the remote shell to copy itself to the remote computer, and then creates a task to run the copy. The Trojan can also be instructed through IRC commands to spread through backdoor ports opened by Mydoom, Bagle, Optix, Netdevil, and other families of malicious software.
Other remote commands may include actions such as:
  • Downloading and executing remote files.
  • Monitoring network traffic.
  • Launching HTTP/HTTPD, SOCKS4, and TFTP/FTP servers.
  • Enabling or disabling DCOM protocol.
  • Retrieving computer configuration information, including Windows logon information, user account information, open shares, file system information, and network connection information.
  • Logging keystrokes.
  • Retrieving CD keys of games.
  • Capturing screens and Webcam shots.
  • Redirecting TCP traffic.
  • Uploading files through FTP.
  • Sending e-mail.
  • Manipulating processes and services.
  • Conducting denial of service (DoS) attacks.
Some variants of Win32/Rbot terminate security-related product processes. Later variants can overwrite the Windows system host file, <system folder>\drivers\etc\hosts, to block access to security-related Web sites. Other variants can install kernel-mode rootkit Virtool/WinNT.FURootkit.A, which hides the Trojan process from Task Manager and other process-viewer applications.


Your computer may be infected with a Win32/Rbot variant if you experience one or more of the following symptoms:
  • The operating system shuts down after displaying a dialog box resembling the following:
    System Shutdown
  • You see an LSA Shell error report dialog box resembling the following:
  • Your computer reboots without user interaction. You may see a system shutdown dialog box resembling the following:


Take the following steps to help prevent infection on your computer:
  • Enable a firewall on your computer.
  • Get the latest computer updates for all your installed software.
  • Use up-to-date antivirus software.
  • Limit user privileges on the computer.
  • Use caution when opening attachments and accepting file transfers.
  • Use caution when clicking on links to web pages.
  • Avoid downloading pirated software.
  • Protect yourself against social engineering attacks.
  • Use strong passwords.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. It is important to install updates for all the software that is installed in your computer. These are usually available from vendor websites.
You can use the Automatic Updates feature in Windows to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
Use up-to-date antivirus software
Most antivirus software can detect and prevent infection by known malicious software. To help protect you from infection, you should always run antivirus software, such as Microsoft Security Essentials, that is updated with the latest signature files. For more information, see
Limit user privileges on the computer
Starting with Windows Vista and Windows 7, Microsoft introduced User Account Control (UAC), which, when enabled, allowed users to run with least user privileges. This scenario limits the possibility of attacks by malware and other threats that require administrative privileges to run.
You can configure UAC in your computer to meet your preferences:
Use caution when opening attachments and accepting file transfers
Exercise caution with email and attachments received from unknown sources, or received unexpectedly from known sources.  Use extreme caution when accepting file transfers from known or unknown sources.
Use caution when clicking on links to web pages
Exercise caution with links to web pages that you receive from unknown sources, especially if the links are to a webpage that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your computer simply by visiting a webpage with harmful content.
Avoid downloading pirated software
Threats may also be bundled with software and files that are available for download on various torrent sites. Downloading "cracked" or "pirated" software from these sites carries not only the risk of being infected with malware, but is also illegal. For more information, see 'The risks of obtaining and using pirated software'.
Protect yourself from social engineering attacks
While attackers may attempt to exploit vulnerabilities in hardware or software to compromise a computer, they also attempt to exploit vulnerabilities in human behavior to do the same. When an attacker attempts to take advantage of human behavior to persuade the affected user to perform an action of the attacker's choice, it is known as 'social engineering'. Essentially, social engineering is an attack against the human interface of the targeted computer. For more information, see 'What is social engineering?'.
Use strong passwords
Attackers may try to gain access to your Windows account by guessing your password. It is therefore important that you use a strong password – one that cannot be easily guessed by an attacker. A strong password is one that has at least eight characters, and combines letters, numbers, and symbols. For more information, see

Alert level: High
This entry was first published on: Mar 18, 2005
This entry was updated on: Apr 17, 2011

This threat is also detected as:
  • W32.Spybot.Worm (Symantec)
  • W32/Sdbot.worm.gen (McAfee)
  • WORM_RBOT (Trend Micro)