A virus may be coded such that it does not cause any suspicious activity from the program it infects. The longer a virus can remain hidden in the system, the more time the virus has to spread and carry out its malicious activity. Assuming the virus code below was written with this in mind, can you find a flaw in the code (the virus writer might call it a "bug")? How could this flaw (or bug) be corrected?
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 :=
{return true if some condition holds}
main: main-program :=
{infect-executable;
if trigger-pulled then do-damage;
goto next;}
next: the-infected-program-now-runs-at-this-point
}