Bike locks aren't made with these types of locks anymore, this was a well known flaw. Kryptonite even recalled these locks and gave away free replacements, which probably cost them millions of dollars.
There are lots of bike lock review sites out there where they test how easy it is to break them. No lock is impenetrable, but the good ones will require a lot of time or loud power tools, something no thief will want to risk when in a well lit high traffic public place. Note: park it in a high traffic, well lit public place! And make it look unappealing (love the buckeye sticker idea, lol).
A good quality U-lock and heavy duty chain through the front wheel is the way to go, but chains aren't very portable so typically a sacrifice is made to use a cable on the go, knowing that cables aren't very secure which puts the front wheel at risk. Having a quality U-lock is vital.