Sony has released an update to the PSP firmware, now bringing it up to version 5.05.
The twist is that, for the moment at least, the only way you can get the update is if you have Japanese game Idolmaster SP, because it's contained on the game's UMD.
This isn't the first time PSP firmware has been released on UMD only; version 3.96 was put out with Hot Shots Golf 2, as Exophase recalls.
With the lack of a changelog in the update installation screen, the exact changes are unclear although it's safe to guess it's a minor update that most likely clears up compatibility issues with the Japanese idol-raising sim.
It's currently unconfirmed whether the update will get a general release, although we've left a message with Sony.