It follows, and is imaginatively named after, the 90s teen horror movies, I Know What You Did Last Summer (1997) and I Still Know What You Did Last Summer" (1998).
Movie info and trailer at IMDB. The DVD hasn't been released yet in Australia but from the trailer, it looks like it spoofs the 1997 original. Completely different cast and production company. Even stars Rachel from Animorphs.
I'm absolutely stunned that this movie was made. Nevertheless, I expect that it should be more of the same. Next thing you know they'll come out with "Even in the Afterlife, I Know What You Did Last Summer" and they can make it a vampire/ghost movie.
Will probably watch all 3 once this one comes out (as I can barely remember now what happened in the first 2).
Speaking of sequels, I thought the Tomorrow, When The War Began (aka "When The War Began") series of novels was finished by the 7th one. But now, 2 more followups have been written. I guess I should have known: if you've ever gotten your hands on the 3rd novel, it mentions on the front cover that it's the last in the "trilogy".
I guess all great trilogies come in threes. Actually, scrub that. Scary Movie and Scream are probably respectively, the most tasteless and boring film series ever. Having watched them in the wrong order, Scream actually appears to be a parody of Scary Movie :) And yes, Scary Movie 1 sends up "I Know What You Did Last Summer" as well.