The Todd Phillips-produced found footage comedy was downloaded illegally nearly 9 million times through BitTorrent, reports TorrentFreak.
Project X takes the number one slot ahead of Mission: Impossible - Ghost Protocol and The Dark Knight Rises, while The Avengers and Sherlock Holmes: A Game of Shadows complete the top five.
"Project X as 'winner' is perhaps the biggest surprise as it's the lowest grossing movie in the top 10 with only $100,931,865," the website said.
Notable movies absent from the top 10 list include Skyfall, The Hunger Games and sci-fi blockbuster Prometheus.
The most-downloaded films of the year via BitTorrent were as follows, with estimated download figures and worldwide box office grosses in brackets:
1. Project X - 8,720,000 ($100,931,865)
2. Mission: Impossible - Ghost Protocol - 8,500,000 ($694,713,380)
3. The Dark Knight Rises - 8,230,000 ($1,081,041,287)
4. The Avengers - 8,110,000 ($1,511,757,910)
5. Sherlock Holmes: A Game of Shadows - 7,850,000 ($543,848,418)
6. 21 Jump Street - 7,590,000 ($201,585,328)
7. The Girl with the Dragon Tattoo - 7,420,000 ($232,617,430)
8. The Dictator - 7,330,000 ($177,547,352)
9. Ice Age: Continental Drift - 6,960,000 ($875,093,094)
10. The Twilight Saga Breaking Dawn - Part 1 - 6,740,000 ($712,171,856)
Digital Spy's top 20 movies of 2012:
