Notwithstanding the provisions of subsections (a)(2) and (b), a person may develop and employ technological means to circumvent a technological measure, or to circumvent protection afforded by a technological measure, in order to enable the identification and analysis under paragraph (1), or for the purpose of enabling interoperability of an independently created computer program with other programs, if such means are necessary to achieve such interoperability, to the extent that doing so does not constitute infringement under this title.

17 U.S. Code § 1201 - Circumvention of copyright protection systems

Has this ever succeeded in court? Has it ever even gotten to court or do people just give up at the first lawyer's letter?

Yes, it has been tested many times, famously for unlicensed video games on consoles.

You do know DMCA is not the only law they can refer to to sue freeloaders, right?