You really have to feel bad for the marketing folks at MARVEL. They went to a lot of trouble to tease and set up the big reveal of the Avengers: Age Of Ultron trailer for next weeks episode of ABC's Agents Of S.H.I.E.L.D. However, less than 12 hours after the big announcement the UK version of the films teaser trailer was leaked onto the internet.
MARVEL's people spent most of the day trying to shut the leak down. Their efforts were largely successful with video's posted on YouTube, but once the video was posted multiple times on European video sharing website DailyMotion, the genie was out of the bottle. By the early evening MARVEL seemed to be raising the white flag as evidenced by their post on Twitter.
After that, MARVEL had little choice. They immediately released the trailer to YouTube. Where that leaves the big reveal for Agents Of SHIELD is unclear, but it's likely that MARVEL will go on as planned.