[chorsestudios]

They could also add a clause to the ToS prohibiting specific activities, but instead it appears they are just cancelling the service entirely.

[latchkey]

https://www.dropbox.com/acceptable_use

use the Services to back up, or as infrastructure for, your own cloud services;

use the storage space provided by the Services as the basis for cryptographic proof-of-space or proof-of-storage, or any similar proof system;

[sanderjd]

They likely already have that clause, but have been unable to enforce it successfully. I would also pull the rip-cord in their shoes. Truly unlimited storage products are a very bad idea.