Maltese_Amoeba

SUMMARY

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.

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low
• Payload Trigger: March 15 or November 1

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

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.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.