Dropbox's privacy policy came under the scanner on Saturday after one of its business customers tweeted that the cloud storage service blocked a file from being shared under U.S. copyright law. The tweet has been retweeted more than 3235 times since then, fueling a concern that Dropbox is scanning users' personal and directly peer-shared files for potential copyright issues.

It all started when designer Darrell Whitelaw generated a sharing link to a video file stored in his account, and then sent it over to one of his friends via a messaging service. But when his friend clicked on the link, the web page displayed the following warning:

Although Whitelaw acknowledged that the file was copyrighted, he was surprised by the warning, which he had never seen before. Also, the original file wasn't deleted from his account, it was just prevented from being shared.

Dropbox also directly reached out to Whitelaw in a tweet:

To which Whitelaw replied: "Not a big deal to me, but apparently some care".

According to Dropbox, the company does not scan your personal files for copyright issues, it rather checks the hash of a shared file against a banned list, and prevents the file from being shared if there's a match. "We have an automated system that then prevents other users from sharing the identical material using another Dropbox link", the company said.

The company also mentions on their website that users should only share files that they have the legal right to share with others.