wow. @dropbox DMCA takedown in personal folders . . . this is new to me. pic.twitter.com/fSKxJUrFus — darrell whitelaw (@darrellwhitelaw) March 30, 2014

Dropbox's copyright policies and terms of service came under scrutiny by the online community over the weekend, after one of its business customers posted a screenshot that showed a file in his personal folder prevented from being shared under U.S. copyright law.

The reaction to the tweet was surprising to its poster, designer Darrell Whitelaw, who told ZDNet in an email: "The world is finding it to be much more interesting than I did."

Whitelaw, who uses the paid-for business version of the online storage service, said he "only posted the screenshot because I'd never seen it before."

The tweet was retweeted more than 2,900 times in less than 24 hours, and received more than 330 responses at the time of writing. Many aired their concerns, while others said they "may need to explore new options."

Dropbox remains one of the most popular online cloud storage and business-based services available , rivalling Apple's iCloud, Microsoft's OneDrive, and enterprise-focused collaboration company Box. In the last couple of years, the company began to offer more for its burgeoning business customer base in order to monetize the service and expand further.

But the company has also faced its fair share of controversies and issues, from multiple outages to data breaches , and as a result, customer trust issues.

The most recent debacle began when Whitelaw generated a sharing link to one .MP4 video file stored in his Dropbox, which he then sent to a friend over a messaging service.

But when the recipient clicked the link, the Dropbox web page warned the recipient:

"Certain files in this folder can't be shared due to a takedown request in accordance with the DMCA."

The Digital Millennium Copyright Act (DMCA), to which the message was referring, allows rights holders to request sites and companies to take down content that it owns, in order to prevent the facilitation of illegal file-sharing.

Dropbox, as a U.S.-based company, must comply with DMCA, as must any other company operating in the U.S.

Dropbox reached out to Whitelaw in a tweet to explain the situation.

@darrellwhitelaw Hey Darrel - content removed under DMCA only affects share-links. DM us if you’re seeing something different so we can help — Dropbox Support (@dropbox_support) March 30, 2014

"Not a big deal to me, but apparently some care," he replied a short time later.

Whitelaw confirmed the video file was copyrighted — implying that it was not his — but was nevertheless surprised by the Dropbox warning, which he said he had never seen before. He also that the files in his Dropbox were not deleted or removed, or restricted from access, but the company are disabling the sharing functionality which can be used to facilitate illegal file-sharing.

Dropbox blocked the file from being shared "immediate[ly]," Whitelaw said.

Dropbox uses deduplication technology, allowing it to store only one copy of files or pieces of files that are the same. In such a case, Whitelaw would likely not have been the recipient of the DMCA complaint. If he stored the exact same file as someone who had received the complaint, his copy of the file would also be prevented from being shared.

"This isn't a Dropbox problem," Whitelaw told ZDNet. "[The company] is just following the laws laid out."

It nevertheless raises the question, once again, about online storage and hosting, storing, and sharing copyrighted material.

A Dropbox spokesperson told ZDNet via email that it "sometimes receive[s] notices to remove links on copyright grounds." These links are processed "according to the law and disable the identified link."

Dropbox confirmed it has an "an automated system that then prevents other users from sharing the identical material using another Dropbox link," which is conducted by comparing file hashes.

The San Francisco, CA-based company did not explain where it receives the details of file hashes from when asked in a follow-up question. However, it's likely music and video industry groups that own the copyright to the files give these to Dropbox and other firms.

"We don't look at the files in your private folders and are committed to keeping your stuff safe," the spokesperson added.

Dropbox makes it clear on its website that users — the paid-for business users and the for-free consumer users — should only share files "that you have the legal right to share with others."

It states:

"Dropbox has adopted a policy of terminating the accounts of users who repeatedly infringe copyright or whose accounts are subject to multiple infringement allegations. If you repeatedly share files that infringe others' copyrights, your account will be terminated."

The company also says that it can take further action, including the removal of content from its servers.

"Dropbox will take whatever action, in its sole discretion, it deems appropriate, including removal of the challenged content from the Site."

For the company, which is expected to make its stock market debut later this year , its bottom-line is simple: Owning a legal copy of a video, music file, or other document does not give users the right to share it — whether you pay for the service or not.

All in all, it was a weekend storm in a teacup. As for Dropbox? It's not the worst way to handle copyright requests under DMCA, but nevertheless unsettling for consumers and companies that use their Dropbox folders like a hard drive.

But as critics have repeatedly warned, the copyright system as is could lead to innocent users suffering if they share a file they have the rights to use, but has been wrongly reported as a DMCA violation.