Según la web PSPHacker un tal Magnus habría abierto la puerta para ejecutar homebrew en las psp de versión 1.5:
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It appears that we may soon have home-brew on 1.5 PSP’s – Don’t get too excited we aren’t sure as of yet. Magnus The Shadow has taken the “must update” eboot and modified it to act like a boot loader from what I understand. – Thanks to psphacker.com for the following article: “Modified Version Must Update File Magnus the Shadow sent us a version of the Must Update file that he worked on. HACKEDEBOOT.PBP is a version that proves the buffer overload method. 1.0EBOOT.PBP is a version that can be run an any PSP. Just put this on your PSP (PSP ver 1.0/1.5, unsure of 1.51) under "PSPGAMEHACK" and rename the .pbp as eboot. Go to GAME on the PSP Menu and then go down to MEMORY STICK Execute the file, you will receive the error message of it being corrupted. Ignore that by pressing "O" and then press "X" again it will bring up the "you must update the ver." window. Don't worry this program in no way changes your PSP He had this to say: The .sfo file (PARAM FILE) in the .pbp can be altered to become a loader, but this can only be done through ELF scripting (Which I can't exactly do). Once an ELF loader is written and replaces the You need to update window section of text i believe a Homebrew app can be run. most likely candidate to is the app Turbo Grafx 16, which will allow us launch other homebrew apps from the PSP! You can download them here.” We will see what comes as a result. Keep your fingers crossed!
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Fuente:
http://www.psphacker.com/2005/05/mustupdate.html 
