Nr Virus

 Virus Name:  Nr 
 Aliases:     Nr.300 
 V Status:    New 
 Discovered:  July, 1995 
 Symptoms:    .COM file growth; file date/time changes; 
              decrease in available free memory 
 Origin:      Unknown 
 Eff Length:  300 Bytes 
 Type Code:   PRhCK - Parasitic Resident .COM Infector 
 Detection Method: NAV, NAVDX, ViruScan, IBMAV, VAlert, AVTK, F-Prot, 
                   NAV/N, IBMAV/N, NShld, NProt, AVTK/N, Innoc 
 Removal Instructions:  Delete infected files 
 General Comments: 
       The Nr or Nr.300 virus was received in July, 1995.  Its origin or 
       point of isolation is unknown.  Nr is a memory resident infector 
       of .COM files, including COMMAND.COM.  It is not related to the 
        NR-481  virus. 
       When the first Nr infected program is executed, this virus will 
       install itself memory resident at the top of system memory but 
       below the 640K DOS boundary, not moving interrupt 12's return. 
       Available free memory, as indicated by the DOS CHKDSK program from 
       DOS 5.0, will have decreased by 320 bytes.  Interrupt 21 will be 
       hooked by the virus in memory. 
       Once the Nr virus is memory resident, it will infect .COM files, 
       including COMMAND.COM, when they are executed.  Infected .COM 
       files will have a file length increase of 300 bytes with the virus 
       being located at the end of the file.  The program's date and time 
       in the DOS disk directory listing will have been updated to the 
       current system date and time when infection occurred.  The following 
       text string is visible within the viral code: 
       Additionally, the text string "Nr" can be found starting in the 
       fourth byte of all infected files. 

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