The trolling is coming from inside the house! Mere emojis can't capture the plugged-in joys of the first hour or so of haunted-Internet teen flick Unfriended, which knifes with dexterous wit The Way We Live Now. Here's a clutch of horny high school dopes hanging out on Skype, getting doxed to death by what seems to be the vengeful ghost of Laura Barns (Heather Sossaman), a young woman who committed suicide a year before. (She had been cyberbullied.)

We see this play out exclusively through the screen of another young woman's laptop: Blaire (Shelley Hennig) indulges in amusingly listless sex-chat with her boyfriend, Mitch (Moses Jacob Storm), scored to songs from the Spotify account she occasionally clicks up from the taskbar. Sometimes, after a scare, she'll Google something related to it. She exchanges tense instant messages — we see her type a truth, hesitate, then erase it in favor of a more politic response. Some of these IMs go to that ghost, of course, which is delicious. She'll hit send and wait a breath while the filmmakers stir up fresh tension from the most banal details of our tech lives: a checked box saying the message has been “seen,” or the agonizingly slow download of a mysterious JPEG. You know the cats that, in most horror films, are good for a fake-out scare or two? Here, ingeniously, their role is played by an autoplay pop-up ad.

So, yes, this movie is 85 minutes of watching someone else use a computer. Nelson Greaves' screenplay cleverly works in YouTube, an antivirus program, Instagram and all the stuttering cam glitches you get from Skype IRL. It occasionally inspires the kind of frustration you feel when looking over a shoulder: No, don't click there, you fool!

The film is adept at the sinking, something's-not-right creepiness too few horror films dig into: Early on, one teen's Facebook is hijacked to post humiliating photos of another friend — a silly idea, but there's a truer terror in the way that that ghost-hacked Facebook account won't let its owner delete the pictures. Anyone who's ever shared something online and then thought better of it can relate, especially once the outside world starts pinging in with “OMG” comments. Director Levan Gabriadze summons up exquisite unease just by the way a cursor darts about a desktop.

But once in a while, especially as Unfriended goes on, the inventive creep-outs get hijacked by plot machinations — it's scary to think the angry dead might hijack your social media sites, but it's not at all when, at one point, they eliminate the forward-message functionality of the heroine's Gmail. And not all are entirely credible: At my screening, a woman near me scoffed, “Why do they all have fucking printers?”

Do white, middle-class California teenagers have printers connected to their MacBooks? Do they even still hang out on Facebook, which increasingly seems like a never-ending Throwback Thursday for millions of over-30s who argue politics with pre-generated meme photos? Unfriended gets so much right in its portrait of how we search, chat, cam and connect that the small things that are off can really dig at you — especially when you consider that this on-the-cheap horror quickie is a more accurate portrayal of online life than anything Hollywood has ever managed. (Remember Peter Parker, in Sony's no-go recent Spider-Mans, searching for clues on Bing?)

Like it or not — and I'm mostly clicking “Like,” myself — Unfriended is the one movie from 2015 you'll always be able to look back at and feel something of what life was like back when, even if you're not a cyberbullying white teen.

The story is moralistic, in the way of dumb multiplex horror. Don't want to be killed in ridiculous/inventive ways in flickering cam footage as your friends scream and refresh the feed? Then don't harass and shame young women online. It's of-the-moment enough that, as one dude-bro chucklehead gets offed, you can imagine him hollering, “It's about ethics in game journalism!”

The revenge is nasty and stupid, of course — the film makes clear that the kids' bullying was rooted in insecurity, in herd mentality, in the dirty thrill of online anonymity. The kids are punished at their laptops for sins that feel everyday, the kind of things real kids have to train themselves not to do. In this sense, the film is prescriptive, even humane. Unlike the Friday the 13th movies, where you could get killed just for being good-looking and naked, Unfriended at least avenges behavior that does serious social harm: Don't be a troll.

The actors are believable enough in one-note roles, but they shout so much that I was happy to see a few get logged off forever. The film's final reels are weak compared with the opening, a common problem in horror — as usual, once the terrifying thing is fully established, the story reverts to established formula. As the corpses pile up, the script's not clear enough on just why these kids can't get help, or walk away from their computers, and there's occasional time-killing filler. But even then Unfriended will sucker-punch you with a clever gag or a wicked game: That ghost forces the kids into excruciating truth-telling, and the payoff to that nonsense about everybody having a printer might be the movie's best shock.

Like those of The Blair Witch Project and Paranormal Activity — both of which inspire scenes here — Unfriended's techniques are certain to be copy-pasted into imitators, some of which might improve upon it. What might be wonderful is if they were applied to something other than the jubilant murder of morally dubious teens. How about a laptop rom-com?

UNFRIENDED | Directed by Levan Gabriadze | Written by Nelson Greaves | Universal | Citywide

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