I saw Die Hard 4 on Saturday night. The premise is that a gang of bad guys lay waste to US infrastructure by breaking into computer systems, until Bruce Willis beats them up. It was fun. The details of the computer action were predictably laughable --- why can't Hollywood get this right more often than once a decade?
However, the underlying premise isn't all that unrealistic. It seems plausible a really determined and well-funded group could pull off an attack on that scale. In fact they could probably pull off something much more alarming. The US military and other organizations are deploying large numbers of UAVs (robotic planes) and now also armed robotic ground units. Of course they work hard to protect the command and control structure but given the state of computer systems today there must be vulnerabilities, especially if someone could insert a human spy. Internet crooks taking control of a battalion of robotic soldiers doesn't really bear thinking about. That'd be a great way for a hostile power to negate the US military advantage... and an interesting movie premise!
There's another great hard-science movie premise in this genre: someone should remake Sneakers around the premise that someone has secretly made a breakthrough in quantum computing and implemented Shor's algorithm, giving them the ability to break RSA (i.e. almost all deployed public-key cryptography). The inventor could be either rescued or assassinated by Bruce Willis, depending on how the screenwriters want to play it. Aside from the movie potential, there is also the intriguing likelihood that this will eventually really happen! (Minus the Bruce Willis part.)