Discom Virus

 Virus Name:  Discom 
 V Status:    Rare 
 Discovered:  November, 1990 
 Symptoms:    TSR; .COM & .EXE growth 
 Origin:      Unknown 
 Eff Length:  2,053 Bytes 
 Type Code:   PRsA - Parasitic Resident .COM & .EXE Infector 
 Detection Method:  ViruScan, AVTK, F-Prot, Sweep, ChAV, 
                    IBMAV, NAV, NAVDX, VAlert, PCScan, 
                    NShld, LProt, Sweep/N, Innoc, NProt, AVTK/N, 
                    NAV/N, IBMAV/N 
 Removal Instructions:  Delete infected files 
 General Comments: 
       The Discom virus was submitted in November, 1990.  The location 
       where the sample was isolated is unknown.  Discom is a memory 
       resident infector of .COM and .EXE files, and will not infect 
       This virus is based on the Jerusalem virus, and also contains some 
       code from the Sunday virus.  As such, some anti-viral utilities may 
       identify files infected with this virus as containing both Jerusalem 
       and Sunday.  This virus does not exhibit symptoms or the activation 
       of either the Jerusalem or Sunday viruses. 
       The first time a program infected with the Discom virus is executed, 
       the virus will install itself memory resident as a 2,304 byte low 
       system memory TSR.  Interrupts 08 and 21 will be hooked by the virus. 
       Once memory resident, the virus will infect .COM and .EXE files when 
       they are executed.  Infected .COM files will increase in length by 
       2,053 bytes and have the virus located at the beginning of the 
       infected file.  Infected .EXE files will increase in length by 2,059 
       to 2,068 bytes with the virus being located at the end of the file. 
       All infected files will end with the following hex character string: 
       Unlike many Jerusalem Variants, this virus does not exhibit a system 
       slowdown after being memory resident for 30 minutes, and no "black 
       window" appears.  Discom will, at random intervals, send random 
       characters to the system COM ports, as well as write portions of 
       itself to random sectors on the system hard drive. 

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