A post to the Quarter To Three Forums reveals English screenwriter/game designer/video games journalist Gary Whitta had been working on a script of the Warcraft movie for two years, though it sounds like he's off the project now that Sam Raimi has been signed as its director (thanks superannuation). Word is:

I had actually been working on this for the past two years. Had to keep it under wraps at the time but it doesn't really matter now.

I worked very closely with Legendary and Blizzard to come up with a screenplay that distilled the sprawling Warcraft mythology into a narrative that was easily accessible to the non-player, and everyone was really pleased with the results - I personally thought my last draft of the script in particular was really kick-ass and did a good job of introducing the Warcraft world to non-players while also satisfying hardcore players who knew every nook and cranny of the universe. When Sam expressed interest in the property, however, he had his own pretty specific vision of what he wanted to do story-wise so that's the version they're now pursuing. I'm no longer involved but I wish them all the best with it; so far as I'm concerned Raimi is the best possible director for this.