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Discovered: June 06, 1999
Updated: May 01, 2007 10:34:31 AM
Also Known As: I-Worm.ZippedFiles [Kaspersky], Win32/ExploreZip.Worm [Computer Associates], W32/ExploreZip@MM [McAfee]
Type: Worm
Infection Length: 210,432 bytes
Systems Affected: Windows

Worm.ExploreZip is a worm that contains a malicious payload. The worm utilizes Microsoft Outlook, Outlook Express, or Exchange to mail itself out by replying to unread messages in your Inbox. The email attachment is Zipped_files.exe.

The worm also searches mapped drives and networked computers for Windows installations. If found, it copies itself to the \Windows folder of the remote computer and then modifies the Win.ini file of the infected computer.

On January 8, 2003, Security Response discovered a packed variant of this threat which exhibits the same characteristics. Protection will be available for this new variant in virus definitions dated 1/8/2003 with a version number of 50108q (20030108.017) or greater.

Antivirus Protection Dates

  • Initial Rapid Release version June 09, 1999
  • Latest Rapid Release version November 04, 2019 revision 019
  • Initial Daily Certified version June 09, 1999
  • Latest Daily Certified version November 04, 2019 revision 065
  • Initial Weekly Certified release date June 09, 1999

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

Technical Description

The payload of the worm destroys any file with the extension .h, .c, .cpp, .asm, .doc, .ppt, or .xls on the hard disk of the infected computer, any mapped drives, and any network computers that are accessible when it is executed. This continues to occur until the worm is removed.

You may receive the worm as an attachment named Zipped_files.exe . When run, this executable copies itself to the \Windows\System folder with the file name Explore.exe or to the \Windows folder with the file name _setup.exe. The worm modifies Win.ini or the registry so that Explore.exe is executed each time you start Windows.

The worm was first discovered in Israel and submitted to Symantec Security Response on June 6, 1999.

Worm.ExploreZip uses MAPI commands and Microsoft Outlook, Outlook Express, or Exchange on Windows 95/98/NT to propagate itself.

The worm emails itself as an attachment with the file name Zipped_files.exe in reply to unread messages in your inbox. Once the worm responds to a message in your inbox, it marks the message so it will not respond to the message again. Because of this, the messages appear to the recipients to be replies to their messages. The message contains the following text:

Hi <Recipient Name>!
I received your email and
I shall send you a reply
ASAP. Till then, take a
look at the attached
zipped docs.


<your name>



<your name>

The worm continues to monitor the inbox for new messages and responds accordingly.

Once the attachment is executed, the following message may appear:

The displayed button is the "OK" button and is dependent on the language of the infected operating system. The example shown was taken from a Hebrew language \Windows.

The worm copies itself to the \Windows\System (\System32 on Windows NT) folder with the file name Explore.exe or _setup.exe and also modifies the Win.ini file (Windows 95/98) or the registry (Windows NT) so that the program is executed each time that Windows is started. You may also find this file in the \Windows temporary folder, or the attachments folder, depending on the email program you are using.


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.


Symantec Security Response has provided a small utility named FixExzip.exe to remove the virus from memory and undo the changes made by the worm. Please click here to obtain this tool. This is the recommended method for removing this worm.

If you want to remove this worm manually, follow these steps:

  • If you are running Windows 95/98:
    1. Open the Win.ini file in a text editor such as the System Configuration Editor (Sysedit.exe).
    2. Remove the command C:\Windows\System\Explore.exe or C:\Windows\System\_Setup.exe from the run= line.
    3. Restart the computer.
    4. Delete Explore.exe from the C:\Windows\System folder.
  • If you are running Windows NT:
    1. Start the Registry Editor (Regedit.exe).
    2. Navigate to the following key:


      and remove the entry that refers to "Explore.exe" or _setup.exe."
    3. Restart the computer, or kill the process using Task Manager or Process View (if the file is currently in use.)
    4. Delete Explore.exe from the C:\Winnt\System32 folder.

NOTE: For information on file recovery, see the Norton Utilities document Error: "Cannot open file... if part of a ZIP format backup set..." and the Size of Many Files is Zero .

Writeup By: Eric Chien