WarGames (1983)

Factual error: At the end of the movie WOPR tries to crack the launch-code using brute force. So far so good. When WOPR finds out one digit of the 10 digit code, the first digit locks and the search goes on with the remaining 9 digits. Then he finds the second one, it locks too and so on. Problem is, brute force doesn't work that way. It would be too easy (26 letters and 10 numbers = only 36 possibilities for one digit). Brute-Force works only "all or nothing", you can't sneak your way to the whole code one by one.

Goekhan

Stephen Falken: The whole point was to find a way to practise nuclear war without destroying ourselves. To get the computers to learn from mistakes we couldn't afford to make. Except, I never could get Joshua to learn the most important lesson.
David Lightman: What's that?
Stephen Falken: Futility. That there's a time when you should just give up.
Jennifer: What kind of a lesson is that?
Stephen Falken: Did you ever play tic-tac-toe?
Jennifer: Yeah, of course.
Stephen Falken: But you don't anymore.
Jennifer: No.
Stephen Falken: Why?
Jennifer: Because it's a boring game. It's always a tie.
Stephen Falken: Exactly. There's no way to win. The game itself is pointless! But back at the war room, they believe you can win a nuclear war. That there can be "acceptable losses."

Trivia: Closely listen to the TV playing in the background, when Mathew Broderick comes home from school, before all his trouble starts with the Feds. The local news is on, and is saying "a fire broke out in a prophylactic recycling factory."

Question: Since David told McKittrick that he thought he was only playing a game and at the time didn't know that he hacked into WOPR, McKittrick tells him that they're still on Defcon 4. Why would it still be on Defcon 4 instead of it going back to Defcon 5 after David confessed everything?