Source code for a core component of the iPhone’s software has appeared online in what is described as “the biggest leak in history.”

iBoot, a part of iOS that ensures the device is booting a trusted operating system, was posted to GitHub anonymously. The code could be used by hackers to find vulnerabilities in Apple’s software. The company has already filed a copyright take-down request to have it removed.

Macs are distinctive among the computing fraternity in the melodious chime they make while booting. While PCs that do nothing more than beep might look on enviously, the fact is that the chime isn’t always welcome—boot your MacBook in a library, for example, and several annoyed faces will willingly hand out censure.

Here’s how to turn off the chime. These instructions are created for OS X Lion but should work with older versions of OS X.

One of my biggest concerns about Apple distributing Mac OS X 10.7 Lion via the Mac App store has been resolved. One intrepid Lion beta tester has discovered a hidden secret inside of Lion’s installation application.