Dropbox clarifies how it knows what you are sharing without looking inside

Dropbox, a file-sharing and cloud-storage service, was this week noted to have blocked a user's personal file as it violated the firm's and DMCA's copyrighted file sharing policies. This raised obvious questions about how Dropbox was able to access the file in the first place, and whether it has been going through each and every file shared online or not.

A little investigation however, found the method behind Dropbox's verification practice was actually quite old.

A user on Twitter, @darrellwhitelaw, said on Saturday that Dropbox had blocked one of his files from sharing. The user tweeted: "wow. @dropbox DMCA takedown in personal folders . . . this is new to me", along with a picture showing an empty folder, presumably where the file was stored.

Dropbox's official response to the tweet said: "There have been some questions around how we handle copyright notices. We sometimes receive DMCA notices to remove links on copyright grounds. When we receive these, we process them according to the law and disable the identified link. We have an automated system that then prevents other users from sharing the identical material using another Dropbox link. This is done by comparing file hashes. We don't look at the files in your private folders and are committed to keeping your stuff safe."

Techcrunch has explained the method behind Dropbox's verification process, detailing how the firm catches a copyrighted file and blocks it without actually peeping the content of the file.

It has been understood that every file shared on Dropbox has a unique hash. Hash is the end codes in the link of the file that changes completely even if someone makes a minor change in it, hence making it unique for every file.

It has been noted that as soon as the user shares a file, Dropbox takes the hash of the particular file and cross checks it with its own list of blacklisted copyrighted files. If the file hash matches the one in the blacklist, Dropbox along with the relevant authority blocks the file from being shared.

Notably, the file remains with the user and is not taken down by Dropbox, but the user is only blocked from sharing it with others.