Tentacle

SUMMARY

Tentacle is one of the first viruses to specifically target Windows executable files. Tentacle only infects programs written for 16-bit versions of Windows by direct infection. It does not become memory resident; rather, it loads, infects other files, and passes control back to the host file.

Tentacle contains no destructive payload. It only reproduces by infecting other 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

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

Tentacle first attempts to infect files in the directory from which the host file is run. After it has attempted to infect files in that directory, Tentacle attempts to infect files in the Windows directory.

Tentacle only infects files with the extension .EXE that are true 16-bit Windows executable files (Windows 3.11 and earlier versions). The virus infects almost all NE files it finds.

Tentacle contains the following text approximately 1,950 bytes from the end of an infected file, although it is never displayed:

C:TENTACLE.$$$ C:WINDOWS*.

Our latest Norton AntiVirus virus scanning engine enables Norton AntiVirus to detect viruses in 16-bit Windows executable files. Detection and repair is available for the Tentacle Virus after June 1, 1996 on all supported platforms including DOS, Windows 3.1, Windows 95, Windows NT. Detection is available on Novell NetWare.

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.