W97M.Thus.A

SUMMARY

W97M.Thus.A is a simple macro virus that infects Word 97 documents. It has a payload that triggers on December 13th which will try to delete all files and subdirectories from the root of the C: drive. This virus will also disable the macro virus protection in Word 97.

Protection

• Virus Definitions (Intelligent Updater) September 2, 1999

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

At the top of the viral macro code, it has a comment line "Thus_001". The virus will check this comment line to determine whether the document is already infected or not to avoid multiple infection. This is where the virus gets it name.

Detection and repair for this macro virus was created automatically by SARA (Symantec AntiVirus Research Automation) on Aug 16, 1999 under the auto-generated virus name called W97M.Automat.K virus. The virus name has recently been renamed to W97M.Thus.A virus.

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.