Desperado

SUMMARY

The Desperado virus is an advanced memory-resident virus that will not only infect .COM and .EXE files greater than 5000 bytes, but will also target the file COMMAND.COM.

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
• Target of Infection: Command, .COM, .EXE files

TECHNICAL DETAILS

Due to this virus’s polymorphic code (code that enables the virus code to change itself each time it spreads), infected files will not be infected exactly in the same way; however, they will have the same size.

During the infection process this virus will check the filename of the file being infected to ensure that it does not contain any of the following ASCII strings (the ASCII strings below are contained within the virus body in encrypted format):

• SCAN
• CLEA
• VSHI
• TOOL
• MSAV
• CPAV
• VSAF
• F-PR
• VIRS
• TBAV
• TBSC
• TBCL
• TBUT
• -V
• UTSC
• UT

This virus also contains code that will delete the file CHKLIST.MS should it be found.

Also among the encrypted text mentioned above, the following text can be found:

Desperado Virus - Written in Malmo F02E

As a final note, this virus will not function if the DOS version in use is 3.x or lower.

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.