Call this the little horror movie that could. “Paranormal Activity,” a low-budget horror flick, started with free showings and spread to a wide release after it went viral with fans who marketed the movie on the internet and via social media.

Paranormal Activity didn’t even have a traditional movie trailer to start, but by using a campaign of limited showings (it played in fewer than 200 theaters), and asking people to go online and spread the word… it managed to earn $7.1 million over the weekend and a wider distribution.

Dreamworks snatched up the film two years ago after Paranormal Activity was an audience favorite at the Slamdance festival. They planned to remake it originally, but ultimately decided to keep it as is.

Late night screenings in college towns created a fan buzz – they took to Twitter and Facebook to talk about it and were told to sign in to ParanormalMovie.com to demand theaters in their locations run the film.

And Paranormal Activity is getting rave reviews too, with Entertainment Weekly giving it an A minus and film critic Owen Gleiberman writing “With its this-is-really-happening vibe, ‘Paranormal Activity’ scrapes away 30 years of encrusted nightmare clichés. The fear is real, all right, because the fear is really in you.”