PS2:Mechapwn
Mechapwn is a homebrew software designed to patch the EEPROM of PS2 models with the "dragon[2] Mechacon [1]"
Mechapwn exploits an update feature introduced on the dragon Mechacon, the main purpose of this update system was to reduce the costs of updating the MECHACON software (because this software was stored on an independent ROM, meaning that an update to this software implied decommissioning of all the Sony stock of already programmed ROMs)
As PlayStation 2 models evolved, the capabilities of these patches became more and more powerful, up to the point where DECKARD slims region can be changed by a single byte on EEPROM, amongst other new possibilities, such as enabling the languages of an European/American PS2 on any asian slim.
Mechapwn main purpose is to change the EEPROM encrypted area where the Mechacon update patches are stored, and the patches applied intend to make the console security measures for discs weaker.
Although, some of the security mechanisms remain, because they're stored on the console boot ROM (such as PS2 and PS1 logo decryption, Wich were used to confirm region match between game and console), in this regard, USA and pseudo asian PS2 (Korea, Taiwan and Hong Kong models) are more permissive compared to European, japanese and Chinese models.
It's very important to backup the EEPROM before playing around with mechapwn.
If you loose your backup, you'll have a very hard time trying to restore EEPROM to original state. Because EEPROMs are not only model-specific, but also factory-specific. (Example: applying the stock EEPROM of a 70001 model manufactured on X factory (eg: foxxcomm) into the same model but made on Y factory (eg: kisarasu) will lead to major issues).
The most conflictive part of EEPROM is the MECHACON configurations, not the ones intended for security, but the ones for mechanics controlling (eg: laser movement config).
The homebrew application PS2IDENT can help you determine from Wich factory your PS2 comes from if you need to (or just feel curious).
Notes
[1]: MECHACON is an acronym for MECHAnics CONtroller. In addition to the tasks implicitly described on its name, it's also in charge of security measures. For example: it participates on games, memory card and memory card update authentication.
[2]: Mechacon dragon corresponds to all Mechacon CPUs starting on SCPH-50xxx, Wich were replaced with a new ARM based CPU. Capable of being updated.