While this shouldn't come as a surprise to anyone, given how many times it's happened in the past, a new exploit has been found that allows PlayStation Portable users running firmware editions 2.00-2.80 to run unsigned, howmbrewed code. While at the moment it only runs a Hello World application, the exploit does open the PSP to more complex homebrewed applications as hackers have time to program for the device. It would appear that Sony has also allowed this flaw to exist for some time now, as the same exploit works for every iteration of the 2.xx firmware.
The flaw itself exists in libtiff, the library which the PSP uses to render TIFF images. Using a specially-doctored image, one can load this image with the PSP's photo viewer and then use the result to run custom code on the little handheld. For the time being, the unsigned code runs in User Mode, but the exploit is expected to work in Kernel Mode with all the firmware editions except for 2.80. The hack itself can be downloaded from the link below, at the bottom of their page.