W97M.Este.A

SUMMARY

This Word 97 macro virus has damaging payloads that are triggered on specific dates. This virus attempts to create a file on the hard drive every Monday after September 30, 1999

Protection

• Virus Definitions (Intelligent Updater) July 28, 2000

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: High

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

This virus infects Microsoft Word 97 documents when they are opened. The virus checks whether a file has been infected or not. It disables macro virus protection in Word 97 and removes the Tools > Macro option. If it is Monday and is after September 30, 1999, the virus creates an index of files on the hard drive. It keeps this index in a hidden file called IObuff?.vxd, where ? is a digit between 1 and 5. The digit is randomly selected and determines which files will be indexed and damaged. This virus will attempt to remove the hidden .vxd file after it has been used. Following are descriptions of the damaging actions that this virus performs depending on the file it creates.

IObuff1.vxd: The virus creates an index of all *.doc files on the hard drive. The index file is called IObuff1.vxd and is hidden. The virus then attempts to infect all documents listed in IObuff1.vxd.

IObuff2.vxd: The virus attempts to write two lines of text to all *.bat files on the system. It also attempts to change the command prompt.

IObuff3.vxd: The virus attempts to write four lines of text to all *.sys files on the system. It also adds the lines:

FILES = 1 and BUFFERS = 1"

to the file(s).

IObuff4.vxd: The virus attempts to write six lines of text to all files on the system. This is a very damaging payload.

IObuff5.vxd: If IObuff5.vxd is created, nothing will happen to the system. The author of this virus did not want to use IObuff5.vxd.

The virus also contains other date-triggered events. On the 14th and 28th of every month, it attempts to change the properties of infected documents.

The virus contains numerous additional random events that change different options in Word 97. Replacing the normal.dot with a known clean backup will reset the options the virus modified to their original states.

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.

REMOVAL

Repair all found infections. If found, delete the hidden file IObuff?.vxd, where ? is a digit between 1 and 5. This file is not viral, it is a plain textfile. This file is not All damaged files must be replaced with known clean copies. The normal.dot can also be replaced with a known clean backup in order to restore the options back to the original state.