wow. @dropbox DMCA takedown in personal folders . . . this is new to me. pic.twitter.com/fSKxJUrFus
— darrell whitelaw (@darrellwhitelaw) March 30, 2014
This tweet spread like wildfire, sparking a debate and discussion among tech users about how DropBox knew that the file in question was copyrighted and whether DropBox was invading the privacy of its users and looking at their files.
Despite what some users may say, the fact of the matter is that no, they are not violating any rights of the user nor are they violating any user agreements. They're not even looking at your files at all.
But how is this possible? How did DropBox then know that the file was copyrighted and warranted issuing a DMCA takedown notice?
The answer is simple: DropBox uses an old trick called hashing against a blacklist.
If you're at all familiar with computer science and/or hashing, then this post ends for you here. But if you're not familiar with what hashing is (or would like a refresher), then the rest of this post is for you.