I didn't have a Kryptonite bike lock (U lock), but I was at movies 2 weeks ago, Chos/Strong got the key from me by stealing it from me, and I had to free my bike, and all it took was a hammer and one bash to the latching end (non-key) of the U lock, and it was free. Apparently the hammer bash also works on Kryptonite locks, but these videos show other means of easy defeat for the Kryptonite locks, which I will never buy again.
