No footage of the teaser seems to be available online yet, but news sites described the trailer as a lone knight standing in an alien, desert world with a glowing green sky. After looting a discarded suit of armor, the knight is besieged by creatures coming over the hills. As an orc approaches, swinging his sword down, the trailer then cut to the logo. Although the trailer isn't currently available online, we may see it pop up at some point soon.
Director Duncan Jones made a brief appearance to mention that the trailer is a "mood piece," and that official shooting will begin early next year. While some players may have been doubtful about the eventual existence of the Warcraft film, its eventual existence is growing more certain by the day -- and the teaser definitely has everyone talking. We'll update if the teaser itself shows up online, until then you can read more about it from Superherohype.