It is widely assumed that the "HAL 9000" computer from "2001: A Space Odyssey" (1968) was the most evil computer in any sci-fi film. This is incorrect. HAL wasn't evil. He was confused. He was misunderstood. He made some very bad choices (as he himself admitted). But he wasn't evil per se.
You want an EVIL computer? I won't get into the details of this film right now though it deserves a discussion in depth. The computer in "The Invisible Boy" (1957) takes the evil prize easily. Not only does it use a firmware "upgrade" to enslave Robby the Robot -- yes, the same Robby, same voice, with an obscure time travel tie-in to "Forbidden Planet" (1956) -- but this computer's philosophy is pretty well summed up by this statement it makes near the end of the film:
"I will seek out organic life wherever it may exist down to even the littlest virus which in time might evolve mentality. So at last, all the universe will be cleansed. All will be sterile. All will be myself."
Now that's evil! -L
@lauren Oh, and I agree. I don't see HAL as evil at all. At every step he / it tries to do what's best according to what it knows. It ended up with a psych problem because it was given conflicting directives. Very human, actually.