A few months ago someone started selling some USB devices that would allow you to install third-party software on the PS3 bypassing the security measures behind sony OS. In short, you could rip games and play them from the hard drive without the disk. Later on, similar open source code was able to achieve the same without buying any special usb device: you could in fact use almost any ARM processor, including an android phone or an arduino. Google psgroove.

Sony of course immediately fought back, first banning the altered OS from the game network and then releasing updates that were not compatible with the loophole. OS on the PS3 cannot be downgraded.

Then, the hackerz fought back and again sold a PSdowngrade device that would allow you to go back to a previous version of the Operative system. Same path, an open source version is released called PSgrade (it's on github) but to work it needs a key associated to your own device or.... a master key.