Tequila.A

SUMMARY

The Tequila virus is an advanced memory-resident polymorphic virus, which uses several techniques to hide itself from the user. The virus body is encrypted and the virus changes itself from one infection to the next. Also, this virus uses both read stealthing and size stealthing, which means that an infected area’s size change will not be noticed during the DIR command or when a disk editing program is being used.

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

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

Upon execution of an infected file, the virus will infect the master boot record only. Next time the system is rebooted this virus will be active in memory and infect any .EXE file as it is executed

When this virus triggers, it first displays in the upper left hand corner of the screen a crude graphic with the following words:

Execute: mov ax, FE03 / int 21. Key to go on!.

If the above instructions are executed, the following text is displayed:

Welcome to T. TEQUILA’S latest production

Contact T. TEQUILAP/P.o. Box 543/6312 St’hausen/Switzerland

Loving thoughts to L.I.N.D.A.

BEER and TEQUILA forever !

On infected hard drives a copy of the original master boot record is stored on the last physical sector of the partition of the first hard drive. This virus makes a modification to the hard drive’s partition table, reducing the size of the partition to protect this area.

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.