There is a holodisk called the Turret Override Program, which you obtain by finding a specific Total Hack magazine.
Anytime you use a terminal that has turrets connected to it, you can "load" the override program to get additional options.
There is a short readme file that states that "scrambling" the targeting parameters will cause the turrets to shoot everyone, including the player. I cannot for the life of me get this to work the way I expect. There's also a menu option for remote targeting, that makes it seem like you should be able to tell the turrets to shoot at specific targets, but this has never worked for me either.
How do I use the override program, especially to make the turrets shoot enemies?
Best Answer
There are four options when using the override program:
Sabotage will cause turrets to explode the next time they fire.
Scramble will cause turrets to shoot everyone.
Override will cause the turrets to become friendly to the player and hostile to enemy NPCs.
Remote control doesn't seem to do anything. Every time it's used it seems to fail.
Note that some of the options aren't always available. Sabotage and override have both been observed to disappear when all turrets connected to the terminal have been destroyed, for example, but not every time.
Also note that if you hit the tab key on PC too quickly, the command might not process. Waiting 2-4 seconds is generally a safe bet. (kudos to aslum in the comments) There are also mods available on Nexus that speed up the terminal output and allow the turret commands to process faster.