The Electronic Frontier Foundation (EFF) on Tuesday issued a warning to Texas Instruments (TI) to back-off its legal threats made to calculator enthusiasts. Texas Instruments was responding to hobbyists who reverse engineered the signing keys put into calculators that only allowed certain operating systems to run on the hardware. By installing a modified operating system they were able to unlock new functionality in the calculator’s hardware.

Naturally, they blogged about how they did it and the modifications they were able to install. Texas Instruments apparently didn’t appreciate the work and sent out a flurry of letters demanding the commentary and links to the keys be taken down under the Digital Millennium Copyright Act (DMCA).

However, the EFF says the DMCA “explicitly allows reverse engineering to create interoperable custom software like the programs the hobbyists are using.” In fact, Texas Instruments makes the software freely available on its Web site, the organization argues.

“This is not about copyright infringement.  This is about running your own software on your own device — a calculator you legally bought,” said EFF Civil Liberties Director Jennifer Granick. “Yet TI still issued empty legal threats in an attempt to shut down discussion of this legitimate tinkering. Hobbyists are taking their own tools and making them better, in the best tradition of American innovation.”