Win32/Dumaru is a family of mass-mailing worms that targets certain versions of Microsoft Windows. The worm sends itself as an e-mail attachment to addresses that it finds on the infected computer. The worm runs when the user opens the attachment. Some variants drop a backdoor Trojan. Win32/Dumaru can infect or overwrite files, open ports, connect to an IRC server, release passwords and other confidential information, and receive commands from attackers.

What to do now

To detect and remove this threat and other malicious software that may be installed on your computer, run a full-system scan with an appropriate, up-to-date, security solution. The following Microsoft products will detect and remove this threat:
For more information on antivirus software, see

Threat behavior

When Win32/Dumaru runs, it can copy itself to multiple locations using various file names. It modifies settings so that the worm runs each time Windows starts.
Win32/Dumaru gathers e-mail addresses from the computer, saves them to a file, and sends itself as an e-mail attachment to those addresses. Some variants encode a copy of the executable file in a script that runs if the e-mail is viewed as HTML. The following is an example of e-mail from a Win32/Dumaru variant:
Subject: Use this patch immediately!
Message Body:
Dear friend , use this Internet Explorer patch now!
There are dangerous virus in the Internet now!
More than 500.000 already infected!
Attachment: patch.exe

Win32/Dumaru variants may also perform actions such as the following:
  • Terminate certain processes.
  • Provide proxy services.
  • Open ports to receive commands or download files from attackers.
  • Modify or overwrite the Windows system hosts file.
  • Inject code into processes such as explorer.exe and run the code. The code intercepts certain API calls so that specified files are hidden.
  • Run hidden instances of Internet Explorer to visit certain Web sites.
  • Collect information such as IP addresses, passwords, screen captures, keystrokes, and clipboard contents. The worm saves the information in log files and periodically sends it to some other location.
  • Infect PE-format executable files in the root directory of NTFS partitions on local or network drives using Alternate Data Streams. On FAT32 partitions, such files may be overwritten so that their original content is not recoverable except from backup files.


There may be no readily apparent indications that your computer is infected with a Win32/Dumaru variant. However, your computer may be infected by this worm if you notice any of the following symptoms:
  • Significant slowdowns during normal operation.
  • Increased outbound SMTP traffic.
  • Receiving an attachment in an e-mail that has subject lines like "Use this patch immediately!", "Important information for you. Read it immediately!"


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 webpages.
  • 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 webpages
Exercise caution with links to webpages 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: Severe
This entry was first published on: Apr 07, 2005
This entry was updated on: Apr 17, 2011

This threat is also detected as:
  • W32.Dumaru@mm (Symantec)
  • W32/Dumaru@MM (McAfee)
  • WORM_DUMARU (Trend Micro)
  • Win32.Dumaru (CA)