To those moaning about the end... (SPOILERS)
To those moaning that 'Charlie' got away, you need to open your eyes, contrary to what Hollywood depicts in 99.9% of its movies, the bad guy don't always lose...
Of course, morally speaking he should have been caught and punished. But this isn't an action movie, it's a drama. The parents are portrayed as your typical middle class American parents, there are no vigilante heroes.
Annie as your typical 14 year old insecure teenager. And I have no doubt there are sicko's out there like 'Charlie' who carefully groom young girls whilst hiding behind very sophisticated technology.
The message of the movie (to me) is "this is how the real world is. Bad people get away with bad things, and often there's nothing you can do about it".
Yes, Charlie could have slipped up and been caught, but in a way I'm glad the writers went in the other direction. Obviously that's a poor message, but it's true. And I think it's more important to remind people how messed up the digital world is rather than focus on the movie stereotype of the good guys always saving the day... it's not always the case.