W97M.Class.A.Gen

W97M.Class.A.Gen changes its own code constantly by inserting comments that contain the current user's name, current date and time, and information about the active printer. By using special WordBasic operators, the virus installs its module into Word classes. The virus code is appended as a native Word component. As a result, the virus is not visible in the Tools, Macro menu.

To replicate, the virus creates the file C:\Class.sys. This file can be safely deleted after the system has been disinfected.

W97M.Class.A.Gen activates on the 31st of every month. At this time it displays this message:

This Is Class
o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o
o      VicodinES     /CB    /TNN      o
o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o

Variants
Some of the variants that are in the wild are:

• W97M.Class.B.Gen: Replication and polymorphism is the same as W97M.Class.A. On the 14th of any month after May, it displays the following message:
  
  I think <user name> is a big stupid jerk!
  VicodinES Loves You / Class.Poppy
  
  where <user name> is taken from the user name on the system.
• W97M.Class.C.Gen: Replication and polymorphism is the same as W97M.Class.A. On 14th of any month after May, it displays the following message:
  
  I think <user name> is a big stupid jerk!
  Class.Poppy
  
  where <user name> is taken from the user name on the system.
• W97M.Class.D.Gen: This variant has a different payload. On 14th of any month after May, it displays the following message:
  
  <user name> is a big stupid jerk
  
  where <user name> is taken from the user name on the system.
  A second payload modifies following registry entry:
  
  HKEY_LOCAL_MACHINE,"Software\Microsoft\Windows\CurrentVersion
  
  and changes "RegisteredOwner" to "VicodinES /CB /TNN" and "RegisteredOrganization" to "-(Dr.Diet Mountain Dew)-"
• W97M.Class.E.Gen: Uses a temporary text file, C:\Clinton.sys. The virus contains references to Clinton and Monica throughout the code. At random times (1 of 100), it displays the message:
  
  Monica Blows Clinton! -=News@11=-
  
  On 17th of any month after August, it displays the following message:
  
  Today is Clinton & Monica F___-Fest Day!"

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.

Summary