Threat Description



Category: Malware
Platform: W32
Aliases: Delf.fz, Trojan-PSW.Win32.Delf.fz


Trojan-PSW.Win32.Delf.fz is a delphi application that drops and loads a password stealing component on infected system.


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

Trojan-PSW.Win32.Delf.fz is a PE executable written in delphi. The trojan file is unpacked and about 51 kilobytes long.

Installation to system

When the trojan file is executed, it makes a copies itself as 'explorer.exe' to Windows system folder. It then adds the following registry key to ensure it will be started next time Windows is started:

[HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon\Shell]  "Explorer.exe" = "C:\Windows\system32\Explorer.exe"   

The trojan also adds an entry to the win.ini file using the Windows API call WritePrivateProfileStringA from the Kernel32.dll. The entry will look like this:

[windows]  Load="C:\Windows\system32\Explorer.exe"   

As win.ini is not supported by Windows NT, 2000 and XP, on these operating system the changes will be added to the Registry.

The trojan also drops a file 'htdll.dll' from its resource to Windows system folder. This DLL is is the password stealing component.


Trojan-PSW.Win32.Delf.fz activates the dropped DLL which starts to monitor Internet Explorer for account information (usernames, passwords). The DLL is activated using a fixed URL that is used to later send collected information to trojan author. The DLL can also send collected information using e-mails.

The trojan tries to kill several firewalls and other security related software in the installation phase to make sure the DLL can connect to remote server.

The trojan also tries to download and activate additional component during the installation. At the time of this writing, this component is not available.


F-Secure Anti-Virus detects this trojan with the following update:

Detection Type: PC
Database: 2005-05-04_02

Description Details: Jarkko Turkulainen, May 18th, 2005


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