PPP allows you to protect your PSP with a password. It’s only for 3.40 OE and 3.5x M33 and only for PSP fat, no PSP SLIM!

INSTRUCTIONS :

1) Download the rar. Put PPPF folder into GAME150 folder of your memory stick. Read note.txt!
2) Go to the recovery and activate autoboot option. Press on the exit function of the recovery.
3) Generate your password.txt (with PPP utility) and put it in the PPPF folder which itself is located in the GAME150 folder.
4) Run the application . Later of this, you will have ppp installed or you will have a brick. Use it in your own risk

http://forums.qj.net/f-psp-development-forum-11/t-release-ppp-v03-more-increased-security-123766.html