Computers are everywhere, yet writers of scripts for movies and TV constantly get them wrong. Ludicrously wrong. Good written fiction, especially science fiction, does better, but writers of all kinds need to be careful. You can depart from the real world if you like, but you have to know what you’re doing. Make sure the reader knows it’s intentional.

Here are six ways writers can mess up. Not all of them are completely impossible, but if you use any of them, you at least need to make the scenario plausible.

1. A super-hacker breaks into a system in two minutes. If the system has some glaring weakness, it’s possible. Maybe the superuser password is “password.” Maybe the hacker has inside information. A competently configured system takes time and effort to crack, no matter how brilliant the people attacking it are. Yes, you want to skip the technical stuff and get to what the hacker finds. There are ways to get through it without resorting to “and then magic happens.”

2. After getting into the system, the super-hacker immediately figures out what the Mysterious Software does. You can set up the situation so it’s possible, but entering someone else’s computer is like entering someone else’s house. You don’t know what’s there or where it is. It takes some reconnoitering, and software that does critical things, such as launching missiles, has additional layers of security. We hope.

3. Then the super-hacker can immediately modify the software so it does something else. That’s really hard. Don’t have it happen. Writing code is work. Testing it is necessary to make sure it works right. Especially if it changes the course of missiles. Hopefully the development environment includes a simulator so you can test it without tossing real missiles around, but I’ve got more bad news. The development environment is on some other computer, not the one that tells the missiles what to do. Even villains bent on world domination know that writing and testing software on a computer that can unleash real destruction is a bad idea.

4. The software has just been upgraded, it’s broken, the national infrastructure is threatened, and no one kept a backup of the previous working version. I actually saw a TV show that had that premise. There was a backup, but it was on a plane that couldn’t land, so it had to transmit a copy to a car that was chasing the plane. It was the first episode of a show whose name I can’t remember; I didn’t come back for the second. There are people who don’t do backups, but they usually aren’t put in charge of software development projects. When idiots are in charge of a project, the disaster usually hits before Version 2.

5. One weak point in the Internet lets somebody take an entire city offline. There are many ways to connect to the Internet, especially in a big city. Taking down a major provider can cause serious trouble, but someone going for major damage would do better to attack the DNS root servers. Subverting or disabling them would make it impossible to match IP addresses with domains, messing the Internet up very badly. Naturally, the root servers aren’t easy to attack or take offline. A state actor might be able to try it, and you could have an interesting plot there.

6. Law enforcement can commandeer any device effortlessly. There’s a bit too much truth to this, but don’t overdo it. I saw a show recently where somebody working for the FBI asked for and got control of every surveillance camera in a wide area for a purely personal mission. The only pushback was some grumbles about using so many resources. Abuse can happen, but you should make it look like abuse, not normalize the surveillance state unless that’s your point.

I could go on and on. The point is to know what you’re writing about. Whether it’s computers, orbital mechanics, gay culture, medieval history, or whatever, do your homework.