If you live online, then you can certainly die online, suggests Unfriended, an internet-age horror film where a collection of standard American teenagers don't even have to leave their l bedrooms to come to a bloody end. The film has a clever conceit, unfolding on a computer screen, but it also inserts a commentary on how online culture lets us ditch our morality when the modem starts up.

The movie begins with Californian high school student Blaire (Shelley Hennig), or more specifically her laptop. Her screen fills our screen, and on it she juggles a video link with her boyfriend, Mitch (Moses Jacob Storm), internet searches, text messaging, tunes and social media. YouTube footage of her late friend, Laura Barns (Heather Sossaman), committing public suicide after enduring online ridicule for an embarrassing clip someone uploaded is just another block in the ever-changing digital mosaic.

When the Skype connection grows to include the couple's friends – Jess (Renee Olstead), Ken (Jacob Wysocki) and Adam (Will Peltz) – they're joined by an unknown presence: a ghost in the machine that starts communicating through Laura's dormant accounts. The intruder unsettles the teens even as they search for the culprit, contacting and haranguing their frenemy Val (Courtney Halverson) until something very bad happens to her. OMG.

Forget malware or Russian hackers – a demon is a genuine online peril, and the film's entity keeps the teens online and mocks their feelings of comparative safety. But it also divides the group, and reveals their hidden roles in Laura's death, when the bully was bullied. Each participant has to admit their private failings to their friends, as if removing a mask. An online community, the film suggests, is just a mob waiting to break bad.

Georgian director Leo Gabriadze massages the many inputs on the single screen, featuring his suitably panicked performers, and the slow refresh rate and intermittent pixilation serves as the digital equivalent of the genre's usual reveal scares. The idea of being safe behind your computer is effectively mocked, with the download bar serving as a countdown to the next crisis.

Unfriended starts to creak by the end, even as the tension is ratcheted up to a hysterical peak, but it's neither bloody nor charged by adrenalin. With the participants sitting at desks or on beds it has a curious inertia, and even with their numbers dropping, Laura keeps her faith in the online world to provide a way out. It turns out, not entirely surprisingly, that if your life is in peril Chatroulette is not the best place to seek urgent assistance.