Apparently Sony may region lock NEW PS3 game releases via the new 3.50 SDK. PS3Gen reports on the story:

While Sony had surprised everyone by not only zoned games on PS3, unlike the PS2 or the PS1, it seems that this idea can be challenged in the near future.

Since the advent of the SDK 3.50, it is possible for official developers restrict their PlayStation 3 games at a specific region.

For information, be aware that verification of the region of the disc was in fact quietly implemented since the 3.30 firmware but was not yet usable by the studios.

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