[borlak]

SquareWheel explained it very well.

As for the difficulty, you'd be surprised how easy it is. I started picking a few weeks ago for fun and I've been able to pick your basic store bought locks within a couple minutes with the hook tool (where you have to lock each pin individually).

There is another tool, called a 'rake', that tries to set several pins at once -- it basically has several jagged edges, much like a key. With rakes I can beat these locks in a matter of seconds, and I'm a newbie! I'm working on the lower end of locks, but even still, it has made me more wary of home security.