I feel this should be considered a rumor until more than one person confirms it. A member of the WoW Subreddit has posted his journey to Weta Workshop and believes they are working on the Warcraft film.
Weta Workshop is located in Wellington, New Zealand is known for providing practical/special effects in famous films such as LotR, Avatar and District 9.
Here is the Reddit post:
"Yesterday, me and a friend took the tour around the Weta Workshop in Wellington, NZ (famous for the props, practical and special effects in the LotR movies, Avatar and District 9 to name but a few). During the tour, the guide mentioned that they were working on a new fantasy film that they could not disclose. However, during the tour, we noticed what we thought were the tier 2 paladin pauldrons, helm and gauntlets lying on a side table. After the tour, we approached the guide and quietly asked if these were indeed what we thought they were. She gave us a surreptitious wink and said that they weren't, but in such a way as to indicate that in fact they were. She followed it up by saying we were the first ever to guess the identity of the items and film. TL;DR Weta is collaborating with Blizzard on the WoW movie"