Shaker Virus

 Virus Name:  Shaker 
 Aliases:     Prague Joker 
 V Status:    Rare 
 Discovered:  November, 1991 
 Symptoms:    .COM file growth; "shaky" screen effect may be produced; 
              decrease in total system and available free memory 
 Origin:      Prague, Czechoslovakia 
 Eff Length:  512 Bytes 
 Type Code:   PRhCK - Resident Parasitic .COM Infector 
 Detection Method:  ViruScan, Sweep, AVTK, F-Prot, ChAV, 
                    NAV, IBMAV, NAVDX, VAlert, PCScan, 
                    NShld, LProt, Sweep/N, Innoc, NProt, AVTK/N, 
                    NAV/N, IBMAV/N 
 Removal Instructions:  Delete infected files 
 General Comments: 
       The Shaker virus was received in November, 1991.  This virus is 
       reported to have originated in Prague, Czechoslovakia.  Shaker 
       is a memory resident infector of .COM files, including COMMAND.COM. 
       It is based on the BackTime virus, and anti-viral programs may 
       identify it as such. 
       The first time a program infected with the Shaker virus is executed, 
       Shaker 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 528 bytes.  Interrupts 08 and 21 will be hooked 
       by Shaker in memory.  Interrupt 12's return will not have been 
       After Shaker is memory resident, the virus will infect any .COM 
       program when it is executed.  If COMMAND.COM is executed, it will 
       become infected.  Shaker infected programs will have a file 
       length increase of 512 bytes.  The virus will be located at the 
       end of the infected file.  There will be no change to the file's 
       date and time in the DOS disk directory listing.  One text string 
       can be viewed within the viral code in infected programs: 
       Systems infected with Shaker may experience a "shaky" screen effect 
       once the virus is memory resident.  This effect, however, does not 
       occur on all systems. 
       See:   BackTime   Blinker 

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