The battle between the homebrew community and Sony has been a long, bloody fight. With Sony finally playing the legal card against homebrewers, PSP 3D takes a retrospective look at the history of Sony's struggle. They claim that Sony has been getting more desperate, and a bit angrier, as seen by this quote from a Sony programmer: "Overall it's [homebrew] frowned on. Our tech guys have gotten madder and madder lately, and it does void your warranty."
The complete article has tons of interesting tidbits. Of particular interest is the infamous GTA exploit which allowed for homebrew to be run even with the most recent firmware release during that time:
"The GTA hack operated in a way which utilized the game's in-game SYSCALLs (system calls) in order to run arbitrary code. This is why kernal (full PSP hardware/software IO access) mode via the hack was impossible; you are only allowed to code as much as the SYSCALLs availability, therefore, advanced SYSCALLs, like those for VSH (update mode) or kernal mode were unavailable for use, simply because GTA: LCS didn't utilize them. This fact brought upon the problem of concern for Sony's engineers. They'd have to release a firmware update which jumbles up the method of loading SYSCALLs in order to prevent homebrew from being loaded. Not easy stuff, really, especially when you need to maintain the working status of all the retail UMD games already released and sold."[Via PlayStation.com boards]