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Discovered: July 03, 2002
Updated: February 13, 2007 11:39:30 AM
Also Known As: Backdoor.Assasin.10, Backdoor.Assasin.11 [AVP], BKDR_SANISI.A [Trend]
Type: Trojan Horse
Systems Affected: Windows

The Backdoor.Assasin Trojan Horse allows unauthorized access to the infected computer. This Trojan Horse also attempts to terminate the processes of many executables, including various firewall and antivirus programs.

Antivirus Protection Dates

  • Initial Rapid Release version July 03, 2002
  • Latest Rapid Release version May 07, 2019 revision 006
  • Initial Daily Certified version July 03, 2002 revision 036
  • Latest Daily Certified version May 07, 2019 revision 008
  • Initial Weekly Certified release date July 03, 2002

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

Technical Description

Backdoor.Assasin sets up the server for a backdoor access. It connects using sockets.

When Backdoor.Assasin is executed, it does the following:

  1. It displays this error message: Invalid Jpeg Image

    Then it copies itself as \%Windows%\Ms spool32.exe.

    NOTE: %Windows% is a variable. The Trojan locates the \Windows folder (by default, this is C:\Windows or C:\Winnt) and copies itself to that location.
  2. It adds the value:
    Ms Spool32         MS SPOOL32.EXE

    to the registry key:


    and also adds the subkey:


    to the registry key:


    3. Creates the \%Windows%\Ms spool32.dat file. This file contains the file names of executable files whose processes the Trojan attempts to terminate. As
    a result, if successful, the following files cannot be run while the Trojan is active:
    • Agentsvr.exe
    • Ahnsd.exe
    • Alogserv.exe
    • Anti-Trojan.exe
    • Ants.exe
    • Aplica32.exe
    • Apvxdwin.exe
    • Atcon.exe
    • Atupdater.exe
    • Atwatch.exe
    • Autoupdate.exe
    • Avconsol.exe
    • Avgserv9.exe
    • Avp.exe
    • Avp32.exe
    • Avpcc.exe
    • Avpm.exe
    • Avsynmgr.exe
    • Blackd.exe
    • Blackice.exe
    • Cdp.exe
    • Cfiadmin.exe
    • Cfiaudit.exe
    • Cfinet.exe
    • Cfinet32.exe
    • Cleaner.exe
    • Cleaner3.exe
    • Cmgrdian.exe
    • Css 1631.exe
    • Defscangui.exe
    • Defwatch.exe
    • Drwatson.exe
    • Fast.exe
    • Frw.exe
    • Fsav.exe
    • Gbmenu.exe
    • Gbpoll.exe
    • Guard.exe
    • Guarddog.exe
    • Iamapp.exe
    • Iamserv.exe
    • Icload95.exe
    • Icloadnt.exe
    • Icmon.exe
    • Icsupp95.exe
    • Icsuppnt.exe
    • Jammer.exe
    • Lockdown.exe
    • Lockdown2000.exe
    • Luall.exe
    • Lucomserver.exe
    • Mcagent.exe
    • Mcupdate.exe
    • Minilog.exe
    • Monsys32.exe
    • Monsysnt.exe
    • Moolive.exe
    • Msconfig.exe
    • Mssmmc32.exe
    • Navapw32.exe
    • Navw32.exe
    • Ndd32.exe
    • Netstat.exe
    • Nprotect.exe
    • Nsched32.exe
    • Ntvdm.exe
    • Nvarch16.exe
    • Nwtool16.exe
    • Outpost.exe
    • Padmin.exe
    • Pavproxy.exe
    • Pcfwallicon.exe
    • Persfw.exe
    • Poproxy.exe
    • Pview95.exe
    • Qserver.exe
    • Regedit.exe
    • Rtvscn95.exe
    • Rulaunch.exe
    • Safeweb.exe
    • Shedapp.exe
    • Sphinx.exe
    • Spyxx.exe
    • Ss3edit.exe
    • Sysedit.exe
    • Taskmgr.exe
    • Taumon.exe
    • Tc.exe
    • Tca.exe
    • Tcm.exe
    • Tds-3.exe
    • Tds2-98.exe
    • Tds2-Nt.exe
    • Trjscan.exe
    • Update.exe
    • Vbcmserv.exe
    • Vbcons.exe
    • Vpc42.exe
    • Vptray.exe
    • Vsecomr.exe
    • Vshwin32.exe
    • Vsmain.exe
    • Vsmon.exe
    • Vsstat.exe
    • Watchdog.exe
    • Webscanx.exe
    • Wgfe95.exe
    • Wradmin.exe
    • Wrctrl.exe
    • Wrctrl.exe
    • Zapro.exe
    • Zatutor.exe
    • Zonealarm.exe
    • _Avp32.exe
    • _Avpcc.exe
    • _Avpm.exe

    The Trojan disables all the AutoDial connections for the current logon session to avoid the dialing, which may reveal the presence of it.

    A separate thread intercepts the user's keystrokes, locates the window in which the user is currently working (foreground window), copies the text of the title bar of this particular window, and drops the intercepted information into a log file.

    Another thread checks every 10 seconds the connected state of the local system to activate the transmission. As soon as the current system is connected to the Internet to supply the remote client with the connection details, the Trojan uses ICQ/email notification. Once the connection is established, the Trojan listens for the following remote commands to perform:
      • Query/update the Internet Explorer security settings.
      • Update the Internet Explorer start page. This may result in navigation to a Web site with potentially unsafe contents, which may be activated if the relevant security settings were compromised.
      • Open/close CD tray.
      • Capture the screen image with the user's data on it.


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.


These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Update the virus definitions.
  2. Restart the computer in Safe mode.
  3. Run a full system scan and delete all the files detected as Backdoor.Assasin. Delete the file C:\%Windows%\Ms spool32.dat.
  4. Reverse the changes made to the registry.

For details on how to do this, read the following instructions.

Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain the virus definitions. These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate), in the "Protection" section, at the top of this writeup.
  • Downloading the definitions using the Intelligent Updater. The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater), in the "Protection" section, at the top of this writeup.

    The 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.

Restarting the computer in Safe mode
All the Windows 32-bit operating systems, except Windows NT, can be restarted in Safe mode. For instructions on how to do this, read the document, "How to start the computer in Safe Mode ."

Scanning for and deleting the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with Backdoor.Assasin, click Delete.
  4. Using Windows Explorer, delete the file C:\%Windir%\Ms spool32.dat.

Reversing the changes made to the registry

CAUTION : Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry ," for instructions.
  1. Click Start, and then click Run. (The Run dialog box appears.)
  2. Type regedit, and then click OK. (The Registry Editor opens.)
  3. Navigate to the following key:

  4. In the right pane, delete the following value:

    Ms Spool32         MS SPOOL32.EXE
  5. Navigate to the following key:

  6. In the left pane, locate and delete the following subkey:

  7. Click Registry, and then click Exit.

Writeup By: Kaoru Hayashi