Threat description




Virus:W32/Delf.BO is malware that connects to malicious websites. Virus:W32/Delf.BO may download files, or get instructions for its malicious acts.


Automatic action

Depending on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the suspect file, or ask you for a desired action.

More scanning & removal options

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

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Technical Details

Once Virus:W32/Delf.BO has been executed, it will display a non-malicious file. Typically, office documents, text files, or log files. The clean file is dropped into the following folder:

  • %temp%\PrgStart

Virus:W32/Delf.BO drops the following malicious file component in the Windows directory:

  • reloc32.exe
  • svhst32.exe

It also drops the following files in the Windows System Directory:

  • updates.exe
  • wandrv.exe

Moreover, it also drops the following file in the Startup folder:

  • SQLNET.exe

Malicious drop files may use the following parameters to execute:

  • -O
  • -RS
  • -A
  • -V

To enable its automatic execution upon boot up it adds the following autostart registry entries:

  • HKLM\Software\Microsoft\Windows\CurrentVersion\RunOnce "Install part II" = "%sysdir%\updates.exe -o"
  • HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices\ "Memory relocation service" = "%windir%\reloc32.exe -rs"
  • HKLM\Software\Microsoft\Windows\CurrentVersion\Run "Microsoft Server Process" = "%windir%\svhst32.exe -a"

Delf.BO modifies the default entry for the program used to open the clean file and executes itself upon opening the same file extension of the clean file.

Example for .TXT files:

  • HCR\txtfile\shell\open\command Original data: %sysdir%\NOTEPAD.EXE %1 New data: %sysdir%\notepd.exe "-v" "%1"

Along with adding or modifying registry entries for its autostart technique, it also adds the following entry in "%windir%\win.ini"

  • "%sysdir%\wandrv.exe"

This is under the following criteria:

  • Name = "windows"
  • Key = "run"

It may connect to the following domain to download other files:


Note: As of this writing the domains above are unavailable. It checks for Internet connection by querying the following site:


It has a backdoor/proxy server functionality that may use the following commands:

  • HEAD
  • POST
  • PUT

Virus:W32/Delf.BO also connects to the following URL:


F-Secure Anti-Virus detects this malware with the following updates:

Detection Type: PC

Database: 2007-05-02_02

Description Created: 2007-05-14 11:50:04.0

Description Last Modified: 2007-05-14 14:14:57.0

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