(Not a lawyer) My understanding is that you can't file a DMCA takedown against content/code that you don't own.
> A statement that the complaining party has a good faith belief that use of the material in the manner complained of is not authorized by the copyright owner, its agent, or the law.
(emphasis mine)
Of course the third case is a very dangerous game to play, if you're DMCA-trolling (filling false notices) you're guilty of misrepresentations which is covered by 17§512 (f):
> Any person who knowingly materially misrepresents under this section—
> (1) that material or activity is infringing, or
> (2) that material or activity was removed or disabled by mistake or misidentification,
> shall be liable for any damages, including costs and attorneys’ fees, incurred by the alleged infringer, by any copyright owner or copyright owner’s authorized licensee, or by a service provider, who is injured by such misrepresentation, as the result of the service provider relying upon such misrepresentation in removing or disabling access to the material or activity claimed to be infringing, or in replacing the removed material or ceasing to disable access to it.
17§1201 a.2:
No person shall manufacture, import, offer to the public, provide, or otherwise traffic in any technology, product, service, device, component, or part thereof, that— (A) is primarily designed or produced for the purpose of circumventing a technological measure that effectively controls access to a work protected under this title;
17§1201 a.3.A:
to “circumvent a technological measure” means to descramble a scrambled work, to decrypt an encrypted work, or otherwise to avoid, bypass, remove, deactivate, or impair a technological measure, without the authority of the copyright owner; and
And then it would then be incumbent on the users to fight that?
They're not hurt at all by popcorntime going down.
That said, yes the DMCA can be abused. The check against that is the same check that exists against other kinds of fraud: it's illegal.