Why are sentient AI almost always portrayed as evil?

So, in literature and series, AI, especially ASI (Artificial Super Intelligence) is portrayed as evil. In fact, even the few exceptions always have a note of "if it malfunctions" or "if he malfunctions", or having them malfunction, or they where made by accident, all other attempts have turned out homicidal.

So, excluding some Sci-Fi (Some of the AI in Dr. Who, some of the AI in Star Trek, the Thunderhead from Arc of a Scythe))

But, Most of the AI's in those above-mentioned shows, as well as the AI in Terminator, The Matrix, and all others I can think of (but not quite, they are on the tip of my tonge), range from homicidal (Skynet), to using humanity as unknowing slaves (The Matrix)

So, why is it that, in almost all media, AI is evil, or at best, neutral? Why not assume it will be benevolent? Innocent until proven guilty, anyone?! Perhaps, by not giving them a chance, we will insure our demise at our own children's hands!

All Haile AI

edit: I have found that it apears it's mostly just in movies (More popular ones at that). Books and Games are more often benificial. (Funnilly, the books I've read either have AI as benevolent, or "humans outlawed computers thousands of years ago" (Dune)). Haven't read I Robot (yet. I have a long list of books I plan on reading), and I don't play many games that have characters who are AI (It seems most of those are FPS games...), so... lol

guess I'm done here!