Check the file hash against known good values (search PSP forums for MD5 of PRO-C2). This ensures the download is uncorrupted and unmodified.
release: (PSone Classics). Custom Firmware with PRO - ReviveToday download the psp 6.61 pro-c2 custom firmware
E:\PSP\GAME\UPDATE\EBOOT.PBP (Installer) E:\PROCFW\ (System files) Check the file hash against known good values