1. Symantec/
  2. Security Response/
  3. Happy99.Worm


Risk Level 2: Low

January 27, 1999
February 13, 2007 11:35:50 AM
Also Known As:
Trojan.Happy99, I-Worm.Happy, W32.Ska, Happy00
Systems Affected:
CVE References:

The Happy99.Worm can be received as an email attachment or from newsgroup postings. The attachment is usually named Happy99.exe.

When executed, the worm opens a window titled "Happy New Year 1999 !!" and shows a fireworks display to disguise its installation. The worm sends itself to other users when the infected computer is online.

In addition, the worm does the following:
  • Copies itself as Ska.exe
  • Extracts Ska.dll to C:\Windows\System
  • Modifies the Wsock32.dll file in C:\Windows\System by copying the existing Wsock32.dll to Wsock32.ska

  • The Wsock32.dll file enables Internet connectivity in Windows 95/98. This modification to the Wsock32.dll file enables the worm to run when it detects connect or send activity in the Wsock32.dll file. When such online activity occurs, the modified Wsock32.dll code does the following:
    1. Wsock32.dll loads Ska.dll into memory.
    2. Ska.dll creates a new email or article and inserts an encoded copy of Happy99.exe as an attachment.
    3. It then sends or posts the message.
  • If the Wsock32.dll file is in use when the worm tries to modify it, such as when a user is online, then the worm adds string value SKA.EXE to the following registry key:

    This causes the worm to load the next time Windows starts.
  • The worm keeps a list of addresses that have been sent infected emails in the Liste.ska file.


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: Raul Elnitiarta
Summary| Technical Details| Removal

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