Re: When was it found out that Section 31 was i the film?
People who read the Ongoing comic had a really strong feeling the Section 31 was going to be involved before the Countdown to Darkness comic basically confirmed it.
Indeed, the comic adaptation of Return of the Archons featured a group of shady Starfleet officers who everyone believed (and still does, I guess) to be Section 31. Since then it was speculated that they'd be featured in STID.
"Internet message boards aren't as funny today as they were ten years ago. I've stopped reading new posts." -The Simpsons 20th anniversary special.