Thirty Three Virus

 Virus Name:  Thirty Three 
 V Status:    New 
 Discovered:  November, 1993 
 Symptoms:    .COM file growth; file date/time changes; 
              decrease in total system & available free memory 
 Origin:      Unknown 
 Eff Length:  525 Bytes 
 Type Code:   PRtCK - Parasitic Resident .COM Infector 
 Detection Method:  IBMAV, F-Prot, ViruScan, AVTK, Sweep, ChAV, 
                    NAV, NAVDX, VAlert, 
                    Sweep/N, NShld, AVTK/N, IBMAV/N, Innoc, NProt, NAV/N 
 Removal Instructions:  Delete infected files 
 General Comments: 
       The Thirty Three virus was received in November, 1993.  Its origin 
       or point of isolation is unknown.  Thirty Three is a memory resident 
       infector of .COM programs, including COMMAND.COM. 
       When the first Thirty Three infected program is executed, this virus 
       will install itself memory resident at the top of system memory but 
       below the 640K DOS boundary, moving interrupt 12's return.  Total 
       system and available free memory, as indicated by the DOS CHKDSK 
       program, will have decreased by 1,024 bytes.  Interrupt 21 will be 
       hooked by the virus in memory. 
       Once memory resident, the Thirty Three virus will infect .COM 
       programs when they are executed.  Infected programs will have a file 
       length increase of 525 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.  One text string is visible within the 
       viral code: 
       It is located very near the end of all infected files. 

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