This application can crash your Macs clipboard, at least on Snow Leopard 10.6.8 The process to do so is quite simple, but requires a few manual steps. 0. Close all applications that are not vital to this test, i.e. everything except Activity Monitor and XCode. 1. Load the project in XCode and start it. 2. Let it run for a few seconds. You can put a few things into your clipboard to see the output. 3. Kill the application in XCode. 4. You should get the familiar "kill\nquit\nProgram ended with exit code: 0" message. 5. Try to copy something to the clipboard. The application that you do this in will lock up (if not, repeat steps 2--4). In fact, any application that tries to access the system clipboard will freeze up and go into a loop. This can and will include XCode, every browser you have open, every terminal you have open and eventually the Finder. As soon as your Finder freezes, you don't have much chance to save your system. The only thing that helps is a hard shut down. If your Finder isn't frozen yet, you can avoid the shutdown by quickly force-killing every frozen application and logging out. Logging back in will reset the clipboard and give you a clean slate. I have tried debugging into a freezing application, and the code the breaks is already the retrieval of the system clipboard via pb = [NSPasteboard generalPasteboard]; This call will go into a rather tight spin lock, from which it will not return. As to the reason for this, I have no idea. Note that the only reference I could find to a similar phenomenon is a StackOverflow question under http://stackoverflow.com/questions/2796997/crashing-the-os-x-pasteboard