On the DVD commentary Patrick Wilson recalled that while filming on the roof, he had to shoot a scene where he yells, "You're not gonna shoot me," five times. After the third or fourth take someone within earshot - not part of the film crew - called the police thinking an actual attack was occurring.
The screenplay's inspiration came from Japan. Producer David Higgins had read reports of Japanese schoolgirls ambushing men who surfed the Internet for underage dates and later developed the story.
Some working titles were "Vendetta" and "Snip Snip." "Hard Candy" was finally chosen because it implies both sweetness and spice--and because it was slang for an underage girl among Internet pedophiles.
Filmed in 18 days.
Despite the intense emotional and physical content of most rest of the movie, Elliot Page said that one of the hardest scenes to shoot by far was the scene at Nighthawks, where for take after take they had to eat more tiramisu than they could ever want.