What are the differences among the firewalls of Figure 22.1? program V := {goto main; 1234567; subroutine

What are the differences among the firewalls of Figure 22.1?

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program V := {goto main; 1234567; subroutine infect-executable := {loop: file := get-random-executable-file; if (first-line-of-file = 1234567) then goto loop else prepend V to file; } } subroutine do-damage := {whatever damage is to be done} subroutine trigger-pulled := next: main: main-program := {infect-executable; if trigger-pulled then do-damage; goto next; } {return true if some condition holds] Figure 21.1 A Simple Virus