One thing you might not know about hackers is that besides cracking some virtual systems many of them are fond of hacking real world stuff as well. One thing of particular interest for them is naturally locking systems. For instance, lockpicking contests and related talks are a common thing at hacker conferences such as DEF CON or Chaos Communication Congress.
At the recent 32C3 conference in Hamburg, Eric Wustrow, a professor at the University of Colorado, presented a report describing how 3D printers can be used to forge keys. To be precise, for the forgery of keys for pin tumbler locks, which is probably the most common lock system.
Before 3D printing was invented, in order to make a copy of a key one had to be skilled in metalcraft or at least in programming some CNC machine tools. Besides that, restrictions included unavailability of certain blank keys, necessity of physical access to key one wanted to forge and others physical world limitations. Obviously, 3D printing makes everything easier and cheaper, since it transfers some of the problems to digital plane.
But are 3D-printed keys that good to work in real life? As a study shows, not all the substances used in 3D-printing are strong enough, some of them are too flexible, some of them are too fragile. But there certainly are some substances suitable for keys forgery. Moreover, for those who are not sure whether plastic will stand it or not, there are certain 3D-printing services which offer printing in metals such as brass, steel or even titanium.