Source: A report on the unofficial French-language Halo blog Halo.fr.
What we heard: According to Halo.fr, a press release from publishing house Milady regarding the French edition of Halo: Cryptum, the latest novel based on the sci-fi shooter, directly references a Halo film coming in 2012 from Steven Spielberg. Translated into English, the line reads, "A film adaptation is set in 2012. It will be conducted jointly by two heavyweights of American cinema: Steven Spielberg and Dreamworks studio."
This corroborates similar reports from 2009 and 2010 that Dreamworks and Spielberg were resurrecting the property, but this is the first time the rumor has been sourced to an officially sanctioned Halo product.
The concept of Halo making the jump to film is not new. At one point Peter Jackson was overseeing the project with District 9's Neill Blomkamp in the director's chair. After a lengthy preproduction period, it famously fell through due to budgetary concerns from the studios funding the project, Universal and Fox.
The official story: After inquiry, a representative from Milady told GameSpot, "We should have put more conditional to this sentence because indeed, we do not have any precise confirmation about this project. Sorry if we made you expect something! :)"
[UPDATE]: Microsoft further debunked the news, telling GameSpot, "The information in the press release in question is inaccurate. We have no plans for a Halo feature film right now. Our focus is on developing Halo: Anniversary and Halo 4."
Bogus or not bogus: Bogus. The book people just chose their words poorly.