Last Saturday, a designer named Darrell Whitelaw posted on Twitter a picture showing one of your folders in Dropbox blocked for alleged copyright infringement. The tweet had much impact – certainly more than Whitelaw expected – a lot of people assumed that the lock consists of a new feature or even service staff scour accounts looking for illegal material. But not quite.
As with most of the online services based in the United States, Dropbox needs to be subject to the laws of the DMCA (Digital Millenium Copyright Act) which, among other rules, determines that irregular content is made unavailable if the holder of their rights so requests.
At TechCrunch, the company explained that every time it receives a copyright infringement notification, the link is terminated blocked, but the file remains intact in the user account. It happened in the case of Darrell Whitelaw. This is the way the company found to prevent the file from being shared, and bring him into trouble with the law.
The most interesting part comes now: to prevent users generate new links for blocked materials sharing, Dropbox has implemented a verification system that calculates the hash file. Hashes associated with files protected by law are then recorded in a kind of “black list”.
Thus, if the user attempts to share a previously not available material, the system will do its lock automatically and immediately, because the hash calculation of a file that did not change even when it is a copy, will always result in the same code.
In summary, Dropbox protection system works like this: every time you upload a file to share it, its corresponding hash is calculated; if the code is the same as any of the existing in the block list, sharing is stopped instantly.
It may seem an exaggeration, but this way Dropbox can avoid legal problems and has one gun to prevent links to content stored on their servers are shared on forums or pages download, for example.
In the end, it’s an interesting system that indicates that no employee is at all times checking what is valid or not in user accounts (although this is possible). Nor do we face a new idea: Dropbox uses hashes for years, not only to check illegal content, but also to avoid that there are two or more files exactly like on your servers, saving storage resources.