Thanks to Macy D for the Info : I have released a binary and source package that exploits a flaw in the PS2's handling of a special configuration file. This configuration file, named TITLE.DB, is accessed from the PS2 PS1 driver (located at rom0:PS1DRV).

To make a long story short, the exploit allows anyone with a memory card and a valid, legal PS1 disc to hijack the boot process and run any piece of code. Absolutely no modification to the system is necessary to use the exploit (my only working PS2 is not moddded, and I have developed and tested the exploit on this machine). All one really needs is a way to send the files to the memory card to enable the exploit.

http://www.0xd6.org/ps2-independence.html