almost no movie has realistic hacking, but i always thought "Hackers" was pretty spot on (for example with the phone phreaking, social engineering).
When i think about movies with unrealistic hacking scenes the following come to mind:
"The Core" has a scene where "rat" whistles into a mobile phone to get free long distance calls (wrong time period)
in "Skyfall" they look through a hex dump and find non-hex characters