Quoting Greg from PSP-Hacks directly :
No videos, no files — just straight facts… My main man, pspjoke, with the assistance of n00b81, has stumbled upon a vulnerability and has fully exploited it. My word; I’ve tested it myself. A few other fortunate folk have as well.
The facts: this save game user-mode hack works on firmware 6.20 and all PSP models, including the 3000 and the PSPgo. That said — it’s obviously a downloadable title. But I won’t go there… We’re under strict orders that we must honour and obey to keep the balance of power intact. Just know unsigned code is indeed running.
Furthermore, an eLoader is planned; pspjoke is working on it. You can follow this thread for ongoing development and discussion surrounding said exploit.
Link to the post :
http://www.psp-hacks.com/2010/02/03/psp-exploit-found-for-all-psp-models-works-on-fw-6-20-too/