JHC.1634

SUMMARY

JHC.1634 is a memory-resident DOS virus that infects the .exe, and .com files, as well as the Master Boot Record (MBR). The size of the infected files are increased by 1,634 bytes.

If the virus is executed from:

• A file, the free conventional memory is reduced by 3,674 bytes.
• The MBR, the total conventional memory is reduced by 4 KB.

JHC.1634 carries a destructive payload. If the virus is executed on June 17th, it attempts to overwrite with blank content any loaded and executed programs.

NOTE: Definitions dated prior to January 31, 2003 may detect this threat as Bloodhound.ResCOM or Bloodhound.ResEXE.

Protection

• Virus Definitions (LiveUpdate™ Weekly) February 5, 2003
• Virus Definitions (Intelligent Updater) January 31, 2003

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: 17th, June
• Payload: Overwrites loaded and executed programs

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When JHC.1634 is executed, it attempts the following:

1. Infect the Master Boot Record (MBR).
2. Move the original MBR to Cylinder 0 Head 0 Sector 6.
3. Overwrite Sector 1 to 6 in Cylinder 0 Head 0.
4. Hook interrupt 21 and 08. After this occurs, this virus will infect any uninfected programs, which were loaded and executed.

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

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions.
2. Run a full system scan and repair all the files and MBRs detected as JHC.1634 or JHC.1634 (b).

For specific details on each of these procedures, read the following instructions.

1. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate), in the "Protection" section, at the top of this writeup.
• Downloading the definitions using the Intelligent Updater. The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater), in the "Protection" section, at the top of this writeup.
  
  The Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

2. Scanning for and repairing the infected files and MBRs

1. Start your Symantec antivirus software and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec corporate antivirus product is set to scan All Files."
2. Run a full system scan.
3. If any files are detected as infected with JHC.1634, click Repair.
4. If any MBRs are detected as infected with JHC.1634 (b), click Repair.