Wm.Twno.D

SUMMARY

The Twno.D virus originated in Taiwan in 1996, and contains three identical macros:

• AutoClose
• AutoNew
• AutoOpen

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: 15th and 25th of each month.
• Payload: Menus renames, files deleted.
• Deletes Files: All files in the DOS directory, and all *.INI files in the WINDOWS directory are deleted if question is answered incorrectly. COMMAND.COM, CONFIG.SYS, MSDOS.SYS and IO.SYS from the root directory are deleted on the 15th of the month.
• Modifies Files: Renames all items on the Word menu bar on the 25th of the month.

Distribution

• Distribution Level: Low
• Target of Infection: Root directory, Windows directory, Word menus, Microsoft Word documents.

TECHNICAL DETAILS

These macros contain code that on the 25 th of the month, renames all the items on the main menu bar for Microsoft Word, and poses a question to the user in Chinese. If the user does not answer correctly, all files in the DOS directory, and all *.INI files in the WINDOWS directory are deleted. It will then display three message boxes in succession. These macros also contain code that unsuccessfully attempts to modify entries in the File and Tools Menus.

If it is the 15th of the month, this virus deletes COMMAND.COM, CONFIG.SYS, MSDOS.SYS and IO.SYS from the root directory of an infected system. All three of the macros are present in infections of the global template, NORMAL.DOT, but standard document infections contain only AutoOpen.

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.