1. Symantec/
  2. Security Response/
  3. Worm.ExploreZip


Risk Level 1: Very Low

June 6, 1999
May 1, 2007 10:34:31 AM
Also Known As:
I-Worm.ZippedFiles [Kaspersky], Win32/ExploreZip.Worm [Computer Associates], W32/ExploreZip@MM [McAfee]
Infection Length:
210,432 bytes
Systems Affected:
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.
Writeup By: Eric Chien
Summary| Technical Details| Removal

Search Threats

Search by name
Example: W32.Beagle.AG@mm
STAR Antimalware Protection Technologies
2016 Internet Security Threat Report, Volume 21
  • Twitter
  • Facebook
  • LinkedIn
  • Google+
  • YouTube