Win32/Rimecud is a family of worms with multiple components that spreads via removable drives, and instant messaging. It also contains backdoor functionality that allows unauthorized access to an affected system.

What to do now

Manual removal is not recommended for this threat. To detect and remove this threat and other malicious software that may have been installed, run a full-system scan with an up-to-date antivirus product such as Microsoft Security Essentials, or the Microsoft Safety Scanner. For more information about using antivirus software, see

Threat behavior

Win32/Rimecud is a family of worms with multiple components that spreads via removable drives, and instant messaging. It also contains backdoor functionality that allows unauthorized access to an affected system.
Win32/Rimecud utilizes two main components - a spreading component and a payload component.
When executed, Rimecud's spreading component opens an Explorer window in the folder it was executed from.
The worm then drops the payload component in the %Temp% directory as "<string>.PIF" and executes it.
When executed, the payload component copies itself to the following location:
  • c:\recycler\s-1-5-21-<Random Number>\<filename>.exe
For example:
  • c:\recycler\s-1-5-21-2752067127-3165661566-893007534-3655\glps.exe
It also drops the file "Desktop.ini", which is used to display the folder "c:\recycler" in Windows Explorer with the Recycle Bin icon.
It then creates an associated registry entry under HKCU\Software\Microsoft\Windows\CurrentVersion\Run to ensure execution at each Windows start.
The worm then injects its main payload code into the "explorer.exe" process.
Spreads via…
Removable drives
The spreading component of Win32/Rimecud sets up a device notification function, which gets called when a USB device is plugged in or removed from the system.
If found the worm copies itself to the root folder of the located drive and creates an "autorun.inf" file to execute the copy. When the removable or networked drive is accessed from another system with Autorun enabled, the malware is launched automatically. For example, it may create the following files:
  • B:\vshost.exe - copy of itself
  • B:\autorun.inf - autorun file used to execute the worm's copy
The payload component also has the ability to spread via "autorun.inf" when instructed to do so. In this case, the worm copies itself to a removable drive and creates an "autorun.inf" file to execute it, for example:
  • RECYCLER\autorun.exe
  • autorun.inf
When the drive in which the Win32/Rimecud file is accessed, the option to "Open folder to view files" is displayed when the drive is accessed. Hence if Autorun is enabled, two options with this text is displayed (the other being the legitimate option from Windows), which may confuse the user. One of these options displays the files in the drive using Windows Explorer (this is the legitimate option from Windows), while the other runs the malware (this is the malicious option), while also opening Windows Explorer.
Instant Messenger
Rimecud's spreading component spreads via a variety of messaging applications, including the following:
  • Yahoo Messenger
  • ICQ
  • AOL Instant Messenger
  • Skype
It does this by looking for windows associated with the targeted application and clicking on menu items and buttons to paste and send an instant message to the user's contacts. The instant message contains a link to the malware.
The payload component can also be instructed to send links if the infected user has MSN messenger installed. It does this by redirecting the send and WSARecv APIs in the MSN messenger process to its own code. Rimecud then attempts to check for the initiation of a conversation and may paste messages specified by the attacker into conversations. This can include links to copies of the worm or other malware.
Allows backdoor access and control
The malware opens a UDP connection to a remote server on port 7006. For example, in the wild, we have observed the following remote hosts being contacted in this manner:
The malware can then be instructed to perform any of the following actions:
  • Check the version of the malware
  • Patch MSN Messenger to insert messages
  • Initiate/Stop spreading via removable drives using the payload component
  • Initiate/Stop flooding a remote host (causing a Denial of Service condition)
  • Initiate/Stop scanning on the affected network for machines using VNC
  • Get the location of the following common Peer to Peer (P2P) File sharing programs, and download files to that location:
    • Ares
    • Bearshare
    • iMesh
    • Shareazza
    • Kazza
    • DC++
    • Emule
    • Emule Plus
    • Limewire
  • Steal passwords and sensitive data from protected storage saved by the Web Browser
  • Download and execute arbitrary executable files to the %temp% directory
  • Download and execute files/Update itself
  • Download and execute scripts or commands / direct to a remote host
Analysis by Ray Roberts and Marian Radu


There are no obvious symptoms that indicate the presence of this malware on an affected machine.


Take the following steps to help prevent infection on your system:
  • Enable a firewall on your computer.
  • Get the latest computer updates for all your installed software.
  • Use up-to-date antivirus software.
  • 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 Web sites.
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
Use caution when opening attachments and accepting file transfers
Exercise caution with e-mail 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 Web page that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your system simply by visiting a Web page 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 in order to compromise a system, they also attempt to exploit vulnerabilities in human behavior in order to do the same. When an attacker attempts to take advantage of human behavior in order 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 system. 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 8 characters, and combines letters, numbers, and symbols. For more information, see

Alert level: Severe
This entry was first published on: Dec 14, 2009
This entry was updated on: Apr 17, 2011

This threat is also detected as:
  • Mariposa botnet (other)