Full Address Space Layout Randomization
This feature, inherent in the new Mac OS X Lion, will make it a lot more challenging for cyber criminals to exploit security vulnerabilities.
Specifically, the Address Space Layout Randomization (ASLR) security feature thwarts exploits by randomizing the arrangement position of key data areas, which make it more challenging for hackers to predict target addresses and launch attacks.
While Mac OS X 10.6 Snow Leopard first introduced the ASLR feature, it was limited to libraries, and missed randomizing the stack and heap.
The ASLR feature baked into Mac OS X Lion, however, is fully implemented, covering 32 and 64-bit applications, and is expected to be a big step up from its feline predecessor.