NYB

SUMMARY

NYB is a simple virus that infects Master Boot Records (MBR) and DOS boot sectors (DBS). NYB spreads to a system only when there is an attempt to boot the system from an infected floppy disk.

Protection

• Virus Definitions (Intelligent Updater) February 17, 1995

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
• Target of Infection: DOS

TECHNICAL DETAILS

During the boot process, NYB loads the MBR into memory and checks for infection. After determining that the MBR is not infected, the NYB stores the uninfected MBR at cylinder 0, side 0, sector 17 on the hard disk. Then, NYB places its virus code into the MBR and rewrites the infected MBR to the hard disk at cylinder 0, side 0, sector 1.

Once the boot process is complete and the NYB virus is active in memory, the virus displays its stealthing capabilities by redirecting any disk reads of the infected MBR or DBS to its clean counterpart. (On floppy disks, the original DBS is stored in the last sector of the root directory.) NYB is highly prolific.

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

Read all the instructions before you begin.

CAUTION:

• If you do not correctly perform the steps described in this document, data loss could result. Unless you are completely familiar using the DOS FDISK command, we suggest that you obtain the services of a qualified computer consultant.
• If your computer uses a Dynamic Drive Overlay, or if you are not sure, first follow the instructions in the document, "How to repair a virus when using a dynamic drive overlay or a disk compression utility."
  

Removing the virus

1. Shut down Windows, and then turn off the power. Do not simply press the reset button.
2. Wait 30 seconds for the memory to be cleared.
3. Do only one of the following:
   • If you have a Norton AntiVirus 2001 (or later) CD, and your computer can start from the CD-ROM drive:
     1. Insert the Norton AntiVirus CD in the CD-ROM drive.
     2. Restart the computer and follow the prompts.
     3. Choose to repair all the infections.
     4. Remove the CD from the CD-ROM drive, and then restart the computer.
     5. Start Norton AntiVirus, and then run a full system scan.
        
        
   • If you have a current Rescue Disk set, or can create one on an uninfected computer:
     1. Insert the first, write-protected disk of the Rescue Disk set in the floppy disk drive.
     2. Restart the computer and follow the prompts.
     3. Choose to repair all the infections.
     4. Remove the floppy disk, and then restart the computer.
     5. Start Norton AntiVirus, and then run a full system scan.
        
        
   • If you do not have a clean Rescue disk or a Norton AntiVirus 2001 (or later) CD:
     1. Insert an uninfected, write-protected, bootable disk, which also contains the FDISK program, into the floppy disk drive. Then restart the computer.
     2. Type the following, and then press Enter:
        
        fdisk /mbr
        
        
     3. Remove the floppy disk, and then restart the computer.
     4. Start Norton AntiVirus, and then run a full system scan.