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  4. Trojan-Downloader:W32/Small.DOG

Trojan-Downloader:W32/Small.DOG

Name : Trojan-Downloader:W32/Small.DOG
Detection Names : Trojan-Downloader.Win32.Small.dog
Size:5,637 bytes
Category:Malware
Type:Trojan-Downloader
Platform:W32
Date of Discovery:August 22, 2006

Summary

This type of trojan secretly downloads malicious files from a remote server, then installs and executes the files.

Disinfection

Allow F-Secure Anti-Virus to disinfect the relevant files.

For more general information on disinfection, please see Removal Instructions.

Additional Details

Trojan-Downloader:W32/Small.DOG secretly downloads malware from a remote site to install and execute on the infected machine. 


Distribution

Small.DOG may be delivered to the system in an infected file attachment accompanying German-language spam e-mail messages, such as below:



The attachment name used is Document.doc.exe. The attachment uses the Microsoft Word icon to disguise its executable nature and deceive the user into believing the attachment is a word document:





Execution

If the user executes the malware by clicking on the attachment, the Trojan creates a new instance of Svchost.exe using itself as the parameter.

It then drops the following file in the Windows System folder:

  •  {Copied filename of any file found on the Windows System directory}{Random character}.exe

Small.DOG attempts to connect to one of the following websites to download an encrypted text file:

  •  http://81.95.147.138/[...].txt
  •  http://docslv.com/gallery/bridge/[...].txt
  •  http://dreadwolf.net/[...].txt
  •  http://dynafilmes.com.br/imagens/3/[...].txt
  •  http://feldvossundpartner.de/images/[...].txt
  •  http://jobundfit.de/images/[...].txt
  •  http://leads4sales.co.uk/images/main/[...].txt
  •  http://mkpicture.de/images/[...].txt
  •  http://soloaguia.com/imagens/[...].txt
  •  http://spbfp.atlant.ru/sys/[...].txt
  •  http://spbfp.atlant.ru/sys/sys/[...].txt
  •  http://trendbusiness-at-home.de/images/[...].txt

It then decrypts the downloaded text file to reveal the following download path:

  •   apte-hamburg.de/Deutsch/Aktuell/{...}.exe

Small.DOG will then download and execute this file. The downloaded file is detected as Trojan-Spy:W32/BZub.BL


Registry

It installs the following registry entries as its autostart technique:

  •  [HKEY_CURRENT_USER\SYSTEM\CurrentControlSet\Control\Lsa]
      {Special Character}:=7<${Special Character}#72'6S =
      "C:\%WinDirSys%\%FileName%.exe"
  •  [HKEY_CURRENT_USER\Software\Microsoft\OLE]
      {Special Character}:=7<${Special Character}#72'6S =
      "C:\%WinDirSys%\%FileName%.exe"
  •  [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run]
      {Special Character}:=7<${Special Character}#72'6S =
      "C:\%WinDirSys%\%FileName%.exe"
  •  [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunServices]
      {Special Character}:=7<${Special Character}#72'6S =
      "C:\%WinDirSys%\%FileName%.exe"
  •  [HKEY__MACHINE\SOFTWARE\Microsoft\Ole]
      {Special Character}:=7<${Special Character}#72'6S =
      "C:\%WinDirSys%\%FileName%.exe"
  •  [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices]
      {Special Character}:=7<${Special Character}#72'6S =
      "C:\%WinDirSys%\%FileName%.exe"
  •  [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]
      {Special Character}:=7<${Special Character}#72'6S =
      "C:\%WinDirSys%\%FileName%.exe"
  •  [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa]
      {Special Character}:=7<${Special Character}#72'6S =
      "C:\%WinDirSys%\%FileName% .exe"

Note: %WinDirSys% is by default C:\Windows\System32 and %FileName% represents the Copied filename plus the Random character.

Detection

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

[FSAV_Database_Version]
Version = 2006-08-23_01.