Keyed to Differ

Keyed to differ padlocks are simply padlocks that are manufactured with random bitting sequences, no two padlocks from the same batch will work with the same key.

 

Since, as mentioned above, there are a limited number of possible bittings for each lock, at some point padlocks will be made with the same bitting.

 

So theoretically a person could have a key that will open their own and someone else's padlock. But the chances of them finding a padlock of the same size and brand that also has the same bitting is tiny.