if i could Code C++ and worked for Sony, the first thing i would do is to put checks in the next Firmware Update, checking to see if the firmware has been Modified, by a Checksum, simple really, and as a added Protection check the Memory stick itself for any Flashing Software in a EBOOT File!!!!!
If it finds anything Format the Card, and crash the PSP!!!!

Come On Sony, Give Up NOW...........No Way of Beating the Master Hackers