Discovered: March 06, 2002
Updated: February 13, 2007 11:38:26 AM
Also Known As: W32.Etap
Type: Virus


W32.Simile is a very complex virus that uses entry-point obscuring, metamorphism, and polymorphic decryption. It infects files in folders on all fixed and remote drives that are mapped at the time that the virus is executed. The virus contains no destructive payload, but infected files may display messages on certain dates.

Antivirus Protection Dates

  • Initial Rapid Release version March 06, 2002
  • Latest Rapid Release version August 08, 2016 revision 023
  • Initial Daily Certified version March 06, 2002
  • Latest Daily Certified version August 09, 2016 revision 001
  • Initial Weekly Certified release date March 06, 2002

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

Writeup By: Peter Ferrie

Discovered: March 06, 2002
Updated: February 13, 2007 11:38:26 AM
Also Known As: W32.Etap
Type: Virus


When the virus is first executed, it checks the current date. If the host file (the file that is infected with the virus) imports the Windows file User32.dll, then on the 17th of March, June, September, or December, a message is displayed. Depending on the version of the virus, it is either:



or



The case of the text is altered randomly. On May 14, a political message is displayed if the system locale matches a certain language. The virus then rebuilds itself. This process is very advanced, and is capable of both shrinking and expanding its code. This avoids the uncontrolled growth that is common for other metamorphic viruses. After the rebuild is complete, the virus searches for .exe files in the current folder, then in folders on all fixed and remote drives that exist when the virus is executed. Files will not be infected if they are located in a subfolder more than three levels deep, or if the folder name begins with the letter W. For each file that is found, there is a 50 percent chance that it will be ignored. Files will not be infected if they begin with the following:

  • F-
  • PA
  • SC
  • DR
  • NO

or if the letter V appears anywhere in the file name. Due to the way in which the name matching is done, file names that contain certain other characters--for example, those that begin with FM or contain the number 6 are also not infected.

The virus contains many other checks to avoid infecting "goat" files (files that are commonly used to capture viruses). The infection process uses the structure of the host, as well as random factors, to control the placement of the virus body and the decryptor.

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.

Writeup By: Peter Ferrie

Discovered: March 06, 2002
Updated: February 13, 2007 11:38:26 AM
Also Known As: W32.Etap
Type: Virus


Obtain the most recent virus definitions. There are two ways to do this:

    • Run LiveUpdate. LiveUpdate is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time 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 write-up.
    • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. 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 write-up.

      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.
  1. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
  2. Run a full system scan.
  3. Delete all files that are detected as W32.Simile. Replace deleted files from a clean backup or reinstall them.


Writeup By: Peter Ferrie