How Miche2245 from our forums has discovered, there is a vulnerability in the firmware 5.50. On this occasion, he has written an exploit, so far for the Japanese version of Monster Hunter and the English version of Need for Speed: Underground works.
The compatibility with other games of the older term is possible, but was not yet fully tested. You will need the savegame, then rename it.
After execution of the exploits of the HEN to start, so you then either use the custom firmware or Enabler 5:03 GEN install them.
Source: www dot pspgen dot com and www dot Dark-Jack dot com