1988) is a case heard by the United States Court of Appeals for the Fifth Circuit that tested the extent of software copyright.

Vault Corporation created and held the copyright for a program called PROLOK, which provided copy protection for software on floppy disks.

Vault sought preliminary and permanent injunctions against Quaid to prevent them from advertising and selling RAMKEY.

The circuit court disagreed with this argument, writing that the statute does not contain "language to suggest that the copy it permits must be employed for a use intended by the copyright owner."

Sony Corp. of America v. Universal City Studios, Inc. established the "substantial non-infringing use" test for contributory infringement.

Vault argued that the court should instead focus on the qualitative aspect of the copied code because the 30 characters were important to the correct operation of PROLOK.

The circuit court rejected the argument that the copying was qualitatively significant on the basis that PROLOK and RAMKEY "serve opposing functions."

The Act purported to permit certain license agreements to contain "...prohibitions on translating, reverse engineering, decompiling, disassembling, and/or creating derivative works based on the computer software."