Lucky Guess

 is an achievement in Deus Ex: Human Revolution.

Walkthrough
During the side-quest "Smash the State", which you get after convincing Taggart to give you Sandoval's location, you simply have to guess the code (which is 0000) to disarm the bomb instead of hacking it. You can also unlock this achievement by using an Automatic Unlocking Device to defuse the bomb.

If you have unlocked the Icarus Landing System, you can climb the ladder next to the bomb and perform a stun (by holding the left mouse button) to disable it. Alternately, you can use a Gas grenade to disarm the bomb.