Unfriended, film review: A tense poke into the dark extremes of social media

If you spend much of your working or leisure time staring at small computers and tablets, a movie in which the action unfolds on web browser pages, Skype and Facebook in real time might not seem like an appealing prospect. The six main characters here aren't very likeable, either – brattish teenagers from Fresno, California, who all knew a certain Laura Barns (Heather Sossaman).

As the film begins, it is a Monday evening exactly a year since Laura committed suicide after a video of her humiliating herself went viral. Some "creeper Skype dude" has joined in with the friends' online conversation, and they don't know who it is. What does become apparent is that all the friends have "dirty little secrets" – and the interloper is determined to expose them.

The screenplay, by the Harvard graduate Nelson Greaves, is very ingenious if a little contrived. "Do not answer messages from the dead," is a piece of web wisdom the protagonists pick up early on, but then blithely disregard. The real surprise here is that the film, produced by Timur Bekmambetov of Night Watch fame, turns out to be so cinematic. Its sound editing is tremendous. All those ring tones and gurgles that computers use are orchestrated for maximum menace.

The film is also effective as a character study about friends who discover that they don't know each other nearly as well as they thought they did. The film-makers ratchet up the tension in sly fashion. At first, the six high-school friends are blasé and dismissive of their online eavesdropper. Slowly but inexorably, their doubts and fears increase.

They begin to turn against each other – and, during the final reel, there is the predictable lapse into Grand Guignol bloodletting. The one thing they are seemingly incapable of doing is quitting their computers. Unfriended works equally well both as a horror movie for the social-media age and as a cautionary tale about cyber-bullying.