Update at 7:45 by Britton Peele: Though the quality of the initial leak was pretty terrible, Warner Bros. has responded in perhaps the best way the company could have: By just saying, "Screw it," and releasing a high-quality version of the trailer a bit earlier than expected.
Original story: As our Britton Peele (and also all the Internet) reported earlier this week, the teaser for the trailer for Batman vs. Superman was released, and the trailer itself was set to debut at select IMAX theaters Monday. But it looks like a bootlegger (somewhere where they use Portugese subtitles) may have leaked the full trailer a few days early.
It's hard to know right away that this trailer is 100 percent authentic, but it doesn't have that fan-made stink about it, and it does appear to feature the voices of cast members Holly Hunter, Jesse Eisenberg (Lex Luthor) and Jeremy Irons (Alfred), plus a brief glimpse of Ben Affleck appearing to scowl at the cowl.
