Microsoft security software detects and removes this threat. 

This family of trojans can monitor what you do online and send the information to a malicious hacker. They can also redirect you web browser to an attacker-specified URL.

What to do now

The following free Microsoft software detects and removes this threat:

Even if we've already detected and removed this particular threat, running a full scan might find other malware that is hiding on your PC.

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/Claretore is a trojan that injects malicious code into Windows processes to interecept web browser communication, and may monitor user activity and send stolen information to a remote website. The trojan could also redirect the web browser to an attacker-specified URL.


When run, it drops a copy of itself with 'hidden' and 'system' file attributes as the following:

  • %HOMEPATH%\< random character string >-< random character string >.exe (example: "C:\Documents and Settings\Administrator\ec3fd7c0-0.exe")
  • %TEMP%\< random character string >.tmp (example: "C:\Documents and Settings\Administrator\Local Settings\Temp\1455b34a-0.tmp")

The registry is modified to run the trojan at each Windows start as in the following example:
In subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run
Sets value: "Windows Update Server"
With data: "C:\Documents and Settings\Administrator\ec3fd7c0-0.exe"

It may delete itself after installation using MoveFileEx() API that effectively modifies the following registry entry:

In subkey: HKLM\Machine\System\CurrentControlSet\Control\Session Manager
Sets value: "PendingFileRenameOperations"
With data: "%Temp%\<random>.tmp"

It creates several threads to monitor and protect changes in its components such as registry entries and file components by calling RegNotifyChangeKeyValue() and ReadDirectoryChangesW() APIs.

Win32/Claretore injects its code as a DLL into every running process with "kernel32.dll" loaded, for example:

  • explorer.exe
  • csrss.exe
  • winlogon.exe
  • services.exe
  • lsass.exe
  • svchost.exe

This method allows the malware to support being installed on Windows 2000 operating systems and helps in hiding the malware so that it is does not appear present when viewing running processes using Windows Task Manager.


Intercepts web browser communication

Win32/Claretore hooks the following functions in "mswsock.dll" to intercept the browser's Internet communication:

  • WSPCloseSocket
  • WSPSend
  • WSPRecv

The trojan then intercepts every website accessed that also has contains a reference to Google Analytics JavaScript, and replaces the legitimate code with code from an attacker-supplied URL. This may result in fake Google Analytics results and/or inflated advertisement click counts.

For example, a variant of Win32/Claretore was observed to replace references to the Google Analytics JavaScript "" with "<removed>", allowing attacker-specified code to execute.

Communicates with a remote server

Win32/Claretore sends the following details about the affected computer, encrypted using MD5, to an attacker-supplied URL:

  • Machine GUID
  • User logon account name
  • Computer name
  • Windows install date
  • Disk identifier

Analysis by Tim Liu


Alerts from your security software may be the only symptom.


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. Instructions on how to download the latest versions of some common software is available from the following:

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: Mar 01, 2012
This entry was updated on: May 13, 2014

This threat is also detected as:
No known aliases