ELEX II

Hacking requires 15 Intelligence and 15 Cunning to unlock. This will allow you to hack Good locks, and increasing those stats and upgrading the skill will allow you to hack Safety locks. However, as with the lockpicking achievement, you can simply save in front of a safe and hack it, reload your save, and then simply type in the code you learned. Safes are not randomized just like the chests, so this will go extremely quickly from there. In fact, if you check a guide online and know the safe code up front, you don't even need to do the hacking mini-game even once.

The hacking mini-game, in case you do need to use it, is completed by solving a bit of a math problem. Press  after accessing the safe to start the hacking process, and you'll need a few blanks with the greater than (>) and less than (<) signs. Choose numbers that fit the pattern, such as 9>4<6>0 and if you got any numbers correct, they will turn green and stay in place. The remaining numbers will be wiped and you'll get to try again. You get four tries before it kicks you out and you have to start fresh. You don't get locked out permanently and the code doesn't change though, so I'm not sure why they bothered with that.