The original Japanese PSPs would run unencrypted code straight off of memory sticks. Then Sony released firmware 1.50. Firmware 1.50 required ALL code it ran to be encrypted. But there was a flaw. Some people from a group called psp-dev discovered that the PSP firmware only checked for unencrypted code ONCE, when it read the archive with the name of the application, the icon, etc. They determined that by making an archive with NO code in it, the psp would give it the OK because there was NO code in it whatsoever. Then the memory sticks would be swapped, and the PSP code loader would run the code off the second stick. But that wasn't good enough for PSP-DEV. Using a flaw in the FAT driver on PSP they were able to make this work with ONE memory stick. Why? When two folders are placed on the memory stick, one with a percent sign after it containing the archive and one without a percent sign containing the code, the PSP would allow you to select the archive, then the PSP bootstrapper would read the directory without the %, because the PSP bootstrap and FAT driver do not understand % signs.
Here come the lamers