Threat Description

Trojan: W32/Vundo


Category: Malware
Type: Trojan
Platform: W32
Aliases: Trojan:W32/Vundo


Trojan:W32/Vundo is a large family of trojans closely associated with adware program that downloads and displays pop-up advertisements.


Automatic action

Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.

More scanning & removal options

More information on scanning or removal options is available in the documentation for your F-Secure security product on the Downloads section of our Home - Global site.

You may also refer to the Knowledge Base on the F-Secure Community site for more information.

Contact Support

For further assistance, F-Secure customers can request support online via the Request support or the Chat forms on our Home - Global site.

Technical Details

The adware is normally downloaded by users from the websites; these malicious sites are normally promoted by spam e-mails. The Vundo family is often distributed as DLL files. It is known to be bundled with adware and/or spyware programs.

For representative examples of Vundo variants and associated programs:


Malware in the Vundo family are installed without the user's consent as a Browser Helper Objects (BHOs). During installation, the DLL file is dropped in Windows system directory. The file name is randomly generated using 8 alphabetic characters:

  • C:\WINDOWS\system32\{8_random_alpha_char}.dll

Upon execution, the DLL is injected into 2 running processes:

  • Explorer.exe
  • Winlogon.exe

In some variants, several data files are created in the same location as the DLL file's execution. The data files' attributes are set as system file and hidden. The files use random names and the following extensions:

  • ini
  • ini2

Once installed, the trojan modifies Microsoft Internet Explorer's security setting to trust cookie content created by the trojan:

  • [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Browser Helper Objects\ {unique_CLSID}]
  • [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3] {unique_CLSID}="malware_hex_value"

Some variants may also attempt to download and execute arbitrary files from remote websites such as:


The program runs hidden from the user.


During installation, malware in the Vundo family create a registry launch point with a unique Class ID. This launch point automatically starts the DLL when system is restarted.

To find this launch point, navigate to the following registry and look for the malicious file pointed by "InprocServer32" registry key:

  • [HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{unique_CLSID}\InprocServer32] @="C:\WINDOWS\system32\{8_random_alpha_char}.dll"

The program will also make further modifications to load itself at startup:

  • [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ShellExecuteHooks] {unique_CLSID}

For some variants, the following registry keys are also created to load the program whenever the user logs on or off. The keys will use the same DLL file name as its key:

  • [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify\{DLL_file_name}] Asynchronous=dword:00000001 DllName="{DLL_file_name}" Impersonate=dword:00000000 Logon="o" Logoff="f"


Suspect a file or URL was wrongly detected? Submit a sample to our Labs for analysis

Submit Now

Give And Get Advice

Give advice. Get advice. Share the knowledge on our free discussion forum.

Learn More