Ever since Bungie's split from Microsoft, details about the subsequent Halo games (in the main series) have been nonexistent. Well, according to an anonymous Internet blog called The Space Oddity, the rumors about Gearbox taking over the series in Bungie's absence are true.
The author, an employee of an unmentioned third-party game publisher, claims in his post that Microsoft will be announcing the game soon and that the fourth entry in the series will actually be a prequel.
Could Halo 4 be Microsoft's show stopping event at E3 '08? Only time will tell.