Drop Virus

 Virus Name:  Drop 
 V Status:    Rare 
 Discovered:  October, 1992 
 Symptoms:    .COM & .EXE growth; decrease in total system & available free 
              memory; file date/time changes 
 Origin:      USSR 
 Eff Length:  1,131 - 1,163 Bytes 
 Type Code:   PRhAK - Parasitic Resident .COM & .EXE Infector 
 Detection Method:  AVTK, Sweep, F-Prot, ViruScan, IBMAV, 
                    NAV, NAVDX, VAlert, PCScan, ChAV, 
                    Sweep/N, NShld, Innoc, NProt, AVTK/N, NAV/N, IBMAV/N, 
 Removal Instructions:  Delete infected files 
 General Comments: 
       The Drop virus was submitted in October, 1992.  It is from the USSR. 
       Drop is a memory resident infector of .COM and .EXE programs, 
       including COMMAND.COM. 
       The first time a program infected with the Drop virus is executed, 
       Drop will install itself memory resident at the top of system memory 
       but below the 640K DOS boundary.  Total system and available free 
       memory, as indicated by the DOS CHKDSK program, will have decreased 
       by 3,600 bytes.  Interrupt 21 will be hooked by the virus in memory. 
       Once the Drop virus is memory resident, it will infect .COM and 
       .EXE programs when they are executed or opened for any reason. 
       Infected .COM programs will have a file length increase of 1,131 
       bytes.  Infected .EXE programs will have a file length increase of 
       1,153 to 1,163 bytes.  In both cases the virus will be 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.  No text strings are visible within 
       the viral code in infected programs. 
       It is unknown what Drop may do besides replicate. 

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