(6) US5775994 Method for automatically activating a control procedure at a user's game system through a broadcast network when said user's license is

當時想把軟體透過第四台把軟體發佈出去，所以要有軟體保護機制。

Reference by:

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2	7,386,618	Matsushita	Distribution system, distribution apparatus, and reception apparatus for distributing contents having usage expiry
3	6,494,762	Matsushita	Portable electronic subscription device and service