WarGames (1983)

Plot hole: McKittrick says the computer will not accept the launch codes unless they are at DEFCON 1. At the end of the climax the computer is trying to guess the code while they are at DEFCON 1. So why couldn't they just go back to a different DEFCON before the correct code was guessed?

Plot hole: Given the number of possible combinations the launch code could be (over 3600 trillion possibilities) it makes no sense that W.O.P.R cannot process that significantly quicker given how easily it's able to calculate thousands of ICBM impacts, damage inflicted, casualties, etc. for each "War Scenario" at the end as quickly as it does to determine a winner.

Plot hole: Having a launch code that is visible to anyone who passes the control terminal does not make any sense especially given the power behind what that code does (launching of nuclear warheads).

Plot hole: It makes no sense that NORAD would inform the media about the false missile attack since they know at that point it was a simulation and no real danger was at hand.

Plot hole: At the end, the suggestion to unplug W.O.P.R. to prevent the missiles from being launched was actually the right suggestion. Given that W.O.P.R. was guessing the launch code by brute force, the actual order to launch the missiles wouldn't be given until the launch code was determined and therefore the silos would not interpret anything until they received not only the order to launch but with the right launch code.