Discovered: February 01, 2002
Updated: February 13, 2007 11:53:02 AM
Type: Worm


This worm spreads through email and IRC.

Antivirus Protection Dates

  • Initial Rapid Release version February 04, 2002
  • Latest Rapid Release version December 25, 2016 revision 009
  • Initial Daily Certified version February 04, 2002
  • Latest Daily Certified version December 26, 2016 revision 001

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

Writeup By: Gor Nazaryan

Discovered: February 01, 2002
Updated: February 13, 2007 11:53:02 AM
Type: Worm


When W32.Dexter is executed it does the following:

It copies itself to:

  • \Windows\Setup.exe
  • \Windows\Sys#.exe (where # represents a number, for example, Sys8.exe)

Then it adds the value

DX     C:\Windows\Sys#.exe

to the registry keys:

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
HKEY_USER\.Default\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

Either registry entry will cause the worm to run when Windows starts.

The worm then checks a registry key to see if WinZip is installed. If it is, then the worm adds the value:

DX    C:\Progra~1\WINZIP\winzip32.exe -a -r C:\Windows\os#.zip C:\Windows\sys#.exe

to the registry key:

HKEY_USER\.Default\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce

This runs the worm the next time that Windows starts, and it zips the C:\Windows\Sys#.exe file as C:\Windows\Os#.zip. The worm then sends this zip file to other IRC users.

The worm spreads through email by searching for email addresses that are contained in .htm files. It sends itself to the email addresses it finds. The email has the following characteristics:

Subject: One of the following:
  • AVP-Virus-Warning
  • freeware nice game
  • My cool, litle program
  • Special FX screensaver

Message: One of the following:
  • There is a new virus in "The Wild" called "W32/Dexter".  Spreads through e-mail and IRC.A solution is this free  program.Send this message to your friends.
    Thank you,
    AVP Team
    AVP.AutoMailer@avp.com
  • hya, chaeck this cool freeware!
    Crazy Games inc. -New game company
    Crazygames@crazy.com
  • Something I coded.It's cool!
    Your best friend
    jonny@yahoo.com
  • A nice FX-screensaver.Better than the "Matrix" one!
    FX-Demo coder
    FXdemos@opengl.org


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.

Writeup By: Gor Nazaryan

Discovered: February 01, 2002
Updated: February 13, 2007 11:53:02 AM
Type: Worm


To remove the worm, delete files that are detected as W32.Dexter and remove the values that it added to the registry.

To remove the worm:

  1. Run LiveUpdate to make sure that you have the most recent virus definitions.
  2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
  3. Run a full system scan.
  4. Delete all files that are detected as W32.Dexter.

To edit the registry:

CAUTION : We strongly recommend 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 only the keys that are specified. Read the document How to back up 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 each of the following keys:

    HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    HKEY_USER\.Default\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    HKEY_USER\.Default\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce
  4. For each one, in the right pane, look for and delete any of the following values:

    DX     C:\Windows\Sys#.exe
    DX    C:\Progra~1\WINZIP\winzip32.exe -a -r C:\Windows\os#.zip C:\Windows\sys#.exe
  5. Click Registry, and then click Exit.


Writeup By: Gor Nazaryan