Basically every pad lock or combo lock with a U shaped shackle is pretty easy to defeat from what I've seen. On at least three occasions I've removed locks with only what I happened to have at hand when I needed to remove the lock. Two steel rods that comprise part of my old Honda's tire change kit stuffed through the shackle and used in a scissor motion did a nice job of applying enough force. Most of the time if it was that hard to defeat the lock it wouldn't be that hard to break whatever apparatus to which the lock is attached. There are secure lock setups of course, but they tend to be bulky and more expensive. Most of the time locks are just an example of how the honor system works better with a modest deterrent.