For years now, Internet users have accepted the risk of files and content they share through various online services being subject to takedown requests based on the Digital Millennium Copyright Act (DMCA) and/or content-matching algorithms. But users have also gotten used to treating services like Dropbox as their own private, cloud-based file storage and sharing systems, facilitating direct person-to-person file transfer without having to worry. […]
The whole kerfuffle started yesterday evening, when one Darrell Whitelaw tweeted a picture of an error he received when trying to share a link to a Dropbox file via IM. The Dropbox webpage warned him and his friend that “certain files in this folder can’t be shared due to a takedown request in accordance with the DMCA.” […]
Dropbox did confirm to Ars that it checks publicly shared file links against hashes of other files that have been previously subject to successful DMCA requests.
http://arstechnica.com/tech-policy/2014/03/dropbox-clarifies-its-policy-on-reviewing-shared-files-for-dmca-issues/