There has been a lot of interesting PSP hacking going on recently.
Around three weeks ago, the PSP’s UMD format was reported to be hacked, with game ISOs starting to appear, allowing developers to have a look at the internals of PSP games. At around the same time, somebody had come up with a tool for running homebrew code on the PSP. Soon thereafter, several emulators were released: first, a Gameboy emulator, soon thereafter also NES and SNES emulators.
However, there’s an interesting catch to all this hackery: tricking the PSP into running these emulators is currently only possible with the 1.0 Japanese firmware—later versions of the PSP firmware check if the code running on the PSP has been officially approved by Sony, preventing homebrew applications from being executed. In order to discourage users to continue using (or downgrade to) the Japanese 1.0 firmware, Sony now even forces PSP owners to upgrade if they want to play the latest games.
Although I am not sure if this handshaking method is a DRM like technology or merely some sort of obfuscation technique (in the former case, reverse-engineering efforts might clash with anti-circumvention regulations), the reason for its existence is clear: Sony wants to keep strict control over innovations in the PSP aftermarket, in a similar fashion as Microsoft did with its XBOX gaming platform (see also footnote 1906 of Stefan Bechtold’s The Present and Future of Digital Rights Management).