A Master Lock combination lock, like you probably had on your locker in high school, has 64,000 different possible combinations. This sounds like a lot, but to a robotic lock cracker with an infinite amount of patience, no locks are safe.
LockCracker is a project created by students at Franklin W. Olin College of Engineering in Massachusetts that's capable of automatically opening any combination Master Lock, as long as you're willing to sit and watch it for as long as two hours while it tries every conceivable combination. It's probably not fast enough to steal lunch from your classmates, but if you can scout out a number or two, you can input those into the machine and it'll find the combination much faster. In any case, mindful of the potential wait, LockCracker thoughtfully provides you with entertainment:
LockCracker is using what's known as a "brute force" approach to solving a combination lock, and while it's time consuming, it's ideal for a machine. It simply tries every possible combination of numbers, sequentially, guaranteeing that eventually it will hit on the proper number sequence.
It's interesting to think about what other ways might exist to make the process more efficient. For example, with locks where you can set your own combination, trying number sequences that correspond to dates is probably a good place to start. And most combination locks have a little bit of leeway in them, meaning that instead of trying every single number, it may only be necessary to try every other number, or even every third number.
The more you know about locks the scarier they are, in terms of how safe people think they are versus how safe they are in reality, especially when locks involve human fallibility (like combinations). A fun read on this topic can be found in Richard Feynman's biography, the relevant bits of which can be read online here (let's see how long that lasts).