The rumors are flying after NeoGAF user Stumpokapow posted that "Halo 3" along with a list of other titles were found in the Steam Apps database. The Steam apps database is Valve's huge list of applications that may or may not actually make it into Steam. This database is open to anyone that knows how to link to it and websites like http://cdr.xpaw.ru/ can access the database to see what is inside.
On Sunday, Feb. 3rd, 2013, when the list of games were posted on NeoGAF, it wasn't long before fans believed that "Halo 3" was confirmed coming to PC. As the blog for the Steam App database website states, "Actually, no. Not by any stretch of the imagination is it confirmed".
In both cases, there are lots of errors in the Steam Database, some bigger than others, and this might just be one of them. Is it a placeholder and is Halo 3 actually on it's way to Steam? Or is it just another Steam Hub page that one of the publishers made for name-reserveration's sake? Or did some completely different developer need a cover to put a test version of his/her game under? Who knows?!
Up until this point there has been no indication from Microsoft, 343 Industries, or Bungie (former developer of Halo) that "Halo 3" would be coming to the PC. However, this news following recent news to shutdown "Halo 2" PC multiplayer servers and the "Halo 3" event known as The Great Journey, which took place this previous weekend, may be some hope for the players that enjoyed playing "Halo 3" more than the titles that followed it. With this news breaking all over the internet, it might require someone to come forward and make a statement one way or another.
Either way, Halo fans will be waiting with bated breath to hear what Microsoft/343 Industries has to say on the matter.