I posted this to a blog that some friends and I post to. I got bored last night and decided to see how easy it would be for me to bypass the cheap cable lock that I use for my bicycle when I'm out and about on short trips. The end result was interesting:
The first time I performed this shim bypass, it took about 5 minutes from start to finish, including the time spent cutting the shim from the soda can. It didn't take me much longer to do it a second time while taking photographs of the process. I completely destroyed the shim trying to remove it from the lock after the photo shoot. A third attempt took me only two minutes, and that included the time spent cutting a new shim from my soda can.
Shimming works on many other kinds of locks, most notably the less-expensive combination- or key-based padlocks that you'd see in a locker room. In fact, it's often faster and easier to shim a cheap lock than to try manipulating or picking it.
When I have to leave my bicycle locked up for extended periods of time, I use a much heavier lock that's far too cumbersome to just lug around willy-nilly for every little trip. Sometimes, I'll use the heavier lock as well as this cable lock if I feel it'd be beneficial. Thieves are lazy, and will usually choose the path of least resistance. We call it the "low-hanging fruit" theory. Unless there's a huge disparity in the value of things to steal, they'll go after the things with the least amount of protection.