Even though the NPD numbers for December aren’t out yet, Microsoft has already  released some statistics concerning Xbox 360 console and software sales. In terms of hardware the Xbox 360 installed base is currently 17.7 million worldwide. As for software Microsoft repeated that the 360 still has the highest software attach rate at 6.9, a .3 increase since all of the systems’ attach rates were tallied by the NPD in October. During that time the PS3’s attach rate was reportedly 3.58, and the Wii’s 3.44.

Microsoft also announced that Halo 3 has sold 8.1 million copies since September 25, which comes as no surprise since there never was a Halo game that didn’t sell. The one real interesting software sales number was of Mass Effect, which sold 1.6 million copies in only six weeks. No doubt EA is keeping a close eye on those statistics. The full NPD numbers for all three consoles will be released on January 17.