Backdoor.Delf.C

Printer Friendly Page

Discovered: August 12, 2002
Updated: February 13, 2007 11:55:39 AM
Type: Trojan Horse
Systems Affected: Windows


Backdoor.Delf.C is a backdoor Trojan horse that allows unauthorized access to the infected computer. It also stops the processes of some antivirus and firewall software.

Antivirus Protection Dates

  • Initial Rapid Release version August 13, 2002
  • Latest Rapid Release version August 20, 2008 revision 017
  • Initial Daily Certified version August 13, 2002
  • Latest Daily Certified version August 20, 2008 revision 016
  • Initial Weekly Certified release date August 14, 2002

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.


Technical Description


In an attempt to avoid detection, Backdoor.Delf.C stops the following processes of some common antivirus and firewall programs:
ANTITROJAN
ANTI-TROJAN
TAU MONITOR
TAUSCAN
BACKWORK
PROTECTOR
ALIENSKIN
AVX
PC-CILLIN
TDS
LOCKDOWN
HOOKPROTECT
TCACTIVE
CLEANER
MKS_VIR
TBAV
VIRUSAFE
QUICK HEAL
SOPHOS
RAV
VIRUSSCAN
VS_STAT
VIRUS FOUND
CENTINEL VXD
VIRUS PROTECT
ANTI VIRUS
F-AGENT
ANTI-VIRUS
ESAFE
AVAST
ANTIVIRENKIT
RGW32
ANTIVIRUS
ANTIVIRAL
AVP
L0PHTCRACK
MKS_VIRW
MKS_MENU
MKS_MON
PCCILLIN
VPTRAY
AAWIN95
NAVW32
_AVP32
AVP32
_AVPM
AVPM

Backdoor.Delf.C then allows a hacker to access the compromised system without authorization.

The Trojan first makes a backup copy of %windir%\Scanregw.exe as a <random name>.exe; it then copies itself as %windir%\Scanregw.exe to disguise itself as the Windows registry scanner.

NOTE: %windir% is a variable that denotes the folder in which Windows is installed. The normal installation folders are C:\Windows or C:\Winnt.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.


Removal


Obtain the most recent virus definitions. There are two ways to do this:

    • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
    • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.

      Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
  1. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
  2. Run a full system scan.
  3. If any files are detected as infected by Backdoor.Delf.C, click Delete.


Writeup By: Gor Nazaryan