Discovered: January 30, 2003
Updated: February 13, 2007 11:57:40 AM
Type: Virus
Systems Affected: Windows


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.

Antivirus Protection Dates

  • Initial Rapid Release version January 31, 2003
  • Latest Rapid Release version January 31, 2003
  • Initial Daily Certified version January 31, 2003
  • Latest Daily Certified version January 31, 2003
  • Initial Weekly Certified release date February 05, 2003

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Robert X Wang

Discovered: January 30, 2003
Updated: February 13, 2007 11:57:40 AM
Type: Virus
Systems Affected: Windows


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":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • 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.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a 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.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. 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.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

Writeup By: Robert X Wang

Discovered: January 30, 2003
Updated: February 13, 2007 11:57:40 AM
Type: Virus
Systems Affected: Windows


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.
  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.


Writeup By: Robert X Wang