Threat Explorer

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13 February 2007
Also Known As:
Amoeba.2367, Gr

Maltese_Amoeba is a memory-resident .COM and .EXE file infecting virus that uses a polymorphic encryption system to hide the virus body within infected files.

Upon infecting the system, the virus performs a system date check. Should the system month and day fields match either one of the trigger dates, an entire screen of ASCII values (ranging from the beginning of the printable ASCII values to the end) will be displayed to the screen with a color background that includes the entire range of colors. During this operation, the user is locked out of the system.

Also, the virus overwrites the first sector of both the hard drive and any floppy disk in the floppy drive. When the user resets the machine, the virus displays the following text to the screen and locks the system after it is done:

"To see a world in a grain of sand,
And a heaven in a wild flower
Hold Infinity in the palm of your hand
And Eternity in an hour."
THE VIRUS 16/3/91

Located within the encrypted virus body is the following text (this text is never displayed; it’s written to both the first sector of the hard drive and the floppy disk.):

AMOEBA virus by the Hacker Twins© 1991
This is nothing, wait for the release of AMOEBA II-The universal infector, hidden to any eye but ours!
Dedicated to the University of Malta- the worst educational system in the universe and the destroyer of 5X2 years of human life

Since this virus does not use any stealthing techniques, the change in infected file sizes is visible during execution of the DIR command.


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.