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Discovered: November 03, 1999
Updated: February 13, 2007 11:41:37 AM
Also Known As: W32/Dupator [McAfee], Win95.Dupator.1503 [KAV], PE_DUPATOR.1503 [Trend], Mid/W95/Dupator [Sophos]
Type: Virus
Systems Affected: Windows

W95.Dupator.1503 is a virus that appends itself to Windows PE files. It also creates an infected copy of Kernel32.dll in the Windows folder.

NOTE: W95.Dupator.1503 has been known to infect variants of W32.Opaserv.Worm. In files where W95.Dupator.1503 cannot be repaired, the files should be deleted.

What are Portable Executable (PE) files?
PE files are files that are portable across all Microsoft 32-bit operating systems. The same PE-format executable can be executed on any version of Windows 95, 98, Me, NT, 2000, and XP. All PE files are executable, but not all executable files are portable.

A common example of a PE file is a screen saver (.scr) file.

Antivirus Protection Dates

  • Initial Rapid Release version November 03, 1999
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version November 03, 1999
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date November 03, 1999

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

Technical Description

When you execute a file that is infected with W95.Dupator.1503, it does the following:

  • Copies the Kernel32.dll file from the \Windows folder to the \System folder.
  • The virus appends itself to the Kernel32.dll file in the Windows folder and points the exported function call, GetFileAttributesA, to the viral code.
  • Once you have restarted the computer, the virus uses the infected Kernel32.dll to infect the Windows PE files.


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.


Update the virus definitions.

  1. Boot the computer from a clean boot disk.
  2. Run the Norton AntiVirus DOS scanner. Repair all files that are detected as W95.Dupator.1503.

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

To update the virus definitions:
All virus definitions receive full quality assurance testing by Symantec Security Response before being posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions are posted to the LiveUpdate servers once 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 writeup.
  • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and manaually installed. 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 writeup.

    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.

To boot the computer from a boot disk:
  1. Shut down Windows, turn off the power, and then wait 30 seconds. Do not press the reset button.
  2. Insert a DOS boot disk or Windows Startup disk, which you know to be uninfected, into the floppy disk drive.
  3. Restart the computer. It will boot to a command prompt.

To run the Norton AntiVirus DOS scanner:
  1. At the A:\> command prompt, type the following commands, and press Enter after each one:

    dir /s /b \navdx.exe

    This changes to drive C and displays the path to the Norton AntiVirus DOS scanner. If NAV is installed on a different drive, then change to the root of that drive first. The default is C:\Program Files\Norton AntiVirus.
  2. Change to the folder that contains Navdx.exe. You must use short file names. For example, if NAV is installed to C:\Program Files\Norton AntiVirus, then type the following:

    cd progra~1\norton~1
  3. Type the following command:

    navdx /a /doallfiles /repair

    This will repair any files which are detected as infected with W95.Dupator.1503, and which are repairable. All files cannot be repaired.
  4. Type the following command:

    navdx /a /doallfiles /delete

    This will delete any files that could not be repaired in the previous scan. Restore the deleted files from a clean backup; if they are program files, re-install the programs.

    CAUTION: This process can take several hours or more on some computers. Do not attempt to stop the scan after it has started.

Writeup By: Douglas Knowles