The saboteur's basic tool is the Trojan horse,
 a widely trusted program which has been¬
surreptitiously modified to do
 bad things in secret.
 ``Bad things'' range from minor but rankling¬
irritations through theft of
 information to holding users to ransom.
 The inevitable fragilities of operating systems¬
can
 be exploited by constructing programs which¬
behave in some ways like primitive
 living organisms.
 Programs can be written which spread bugs like an¬
epidemic.
 They hide in binary code, effectively¬
undetectable (because nobody ever
 examines binaries).
 They can remain dormant for months or years,¬
perhaps quietly and imperceptibly
 infiltrating their way into the very depths of a¬
system, then suddenly pounce,
 causing irreversible catastrophe.
 A clever and subtle bug\(dg can survive
 recompilation despite the fact that there is no¬
record of it in the source
 program.
 .FN
 \(dg Throughout this article the word ``bug'' is¬
meant to bring to mind a
 concealed snooping device as in espionage, or a¬
micro-organism carrying