Millions of users have downloaded Popcorn Time since the torrent software debuted earlier this year, both for its ease of use and the clean interface that's inspired the “Netflix for pirates” tag line. Yet questions continue to swirl around the torrent client, with users wondering whether the service is legal and the original developer now registering a trademark to prevent imitations from flooding the market.

Simply downloading Popcorn Time isn't a crime, though “Popcorn Time,” like Kleenex's effect on the tissue industry, has become Internet shorthand for illegally streaming Hollywood movies with a certain kind of software. What Popcorn Time, as software, does do is simplify and enable the normally tricky process of copyright infringement by making it possible for users to stream and share Hollywood movies without paying the fees found on legitimate streaming services like iTunes or Netflix.

Other popular clients used to access torrents -- like Vuze and uTorrent, for example -- make it clear to users that they're simultaneously downloading and uploading an individual file, such as a movie. The risk, for pirates nervous about their activity, comes in when they're uploading a file, as they have no choice but to expose their IP addresses, locations and often the WiFi networks being used.

Popcorn Time advises users to be careful to avoid copyright infringement, but does little to make it clear to users they're uploading the very file they're streaming. Internet forums are filled with angry Popcorn Time users who have received copyright infringement letters threatening legal action. The Netflix-like display that's made Popcorn Time more attractive than the Pirate Bay, some assert, also hides the risk that's obvious on more established sites.

“I was under the impression that Popcorn Time was safe ... but I just got forwarded an email from my Internet-service-provider,” one user complained on Reddit. “It was from Warner Bros. and they are pissed that I watched the new “300” movie on Popcorn Time. Any idea how they found out.”

Popcorn Time has faced similar allegations in the past, saying at the time developers “don't expect legal issues” and the software is “an experiment to learn and share.” Now, TorrentFreak said, the client's developers are blaming the confusion on imitators that are using the Popcorn Time brand and seeking to rectify the situation by filing a trademark on the name.

“We strongly believe in the open contributions to the Popcorn Time project and the filing of the trademark wasn't designed to hinder or prohibit the further development of the official Popcorn Time or any other related forks,” an anonymous source told TorrentFreak. “It's wise to attempt to protect the trademark from 'giants' who might come along, sweep up the name, and then bully contributors into nonexistence.”

At least one of those imitators, the popular "Flixtor" site, has already shut down because of pressure from copyright owners.