The minute your PS3 boots up, it runs through 4 stages of security at all times. All 4 stages have secrets that will need to be decoded in order to reach the next stage. So think of hacking the PS3 to be similar to a treasure hunt. You discover the clues and figure out a way to piece them all together to find the treasure. Except in this hunt for the booty, if you mess up one tiny thing, the whole mission collapses and your PS3 could possibly explode into vast reaches of outer space
The first: The Hard Drive
For starters, the PS3 is not easily fooled like its sibling PSP. Sony has encrypted each hard drive to only work with a specific PS3, which eliminates the possibility of switching them out like memory sticks. The hard drive is then read by the PS3 where it makes sure the drive is registered to the specific console. After verifying the hard drive, the PS3 continues to search for needed files to boot up the OS. This is merely the logo that appears or random files hidden in the system that will trigger the "OK" to boot up. The hard drive is built in layers with the "bootflag.dat" being the first file read on each start up, which then leads into the DRM file and finally ... the game files. Several files found in between each of these makes things even more complicated to bypass. We must also note that messing with any of these files will cause the PS3 to read them as missing and not boot up correctly.
The second: The 7th "cell"
If you finally get past the hard drive, you must then face the problems hidden within the actual system itself. We all know the PS3 is a beast with a hearty 7 cells running under the hood as we brag about this on a daily basis. The problem for hackers is how only 6 of these cells are actually accessible, with the 7th cell access being denied to everyone. Not even game developers have access to this 7th cell. Now why is this cell even there if we can't use it? In a simple sentence, the 7th cell runs the PS3 completely on its own. The cell boots the system up, cracks the codes encrypted in all security branches, and finally keeps the OS running while you play a game or do whatever you normally do. Remember how I talked about the PS3 verifying the HDD in relation to the system? This is where that comes into place. The 7th cell is what verifies everything that needs to be unlocked or encrypted.
The third: The Blu-Ray itself
If hackers somehow find a way to hack the hard drive and bypass the 7th cell, there is still one more major problem awaiting for them at the next step. If you haven't heard about Blu-ray, then you are probably thinking PS2 is the shiznit right now and randomly came across this article of the future somehow. Joking aside, Blu-ray is an amazing feature for HD users and a tremendous advancement for all game makers with a massive storage space and fast loading times. However, it is also the biggest problem to every hacker out there. Each Blu-ray disc comes equipped with a special "disc-based" encryption that is stronger than the security we find on DVD. The 128-bit key is hidden within each disc marked as BD-ROM and requires the "special" Blu-ray technology to decrypt it. Does Eboot.bin sound familiar? No? Well for the new guys, this is the file that hides all the required data to run a game or movie, which is very important. Now you can guess what is hidden under the encryption layer of BD. A Blu-ray lens can read the encryption, unlock it, and break it down from a .SELF file and .ELF file for games, where the Eboot file can be shared with the system. Even if this code is bypassed, hackers would have trouble finding ways to boot up a particular file without having the disc inserted.
The fourth: Loss of Warranty
While the PS3 is closed down like the gates at Fort Knox, hackers do occasionally find ways to breach the security of the system. Some hackers have tried to steal passwords, some have tried to destroy the PS3 due to their frustrations of failing, and others randomly do something stupid to make us all laugh. Sony finds out about these hacks, or "attempts" as it were, and immediately issue software updates to protect users like you and I. These updates help protect the PS3 from attacks and are required to access the PlayStation Network. When a PS3 logs into the PSN, it registers on the network with its firmware version. Having faulty firmware will get you banned from the PSN permanently and possibly trigger something to go wrong internally. Hacking the PS3 will also void your warranty and you will no longer be allowed to receive repairs. This final precaution is the 4th and final step Sony has taken to prevent the pirates from hacking your PS3.
http://www.ps3center.net/article/202/1/why-hasnt-the-ps3-been-hacked/