Microsoft last week announced Halo 4, not that it owed the halo4.com domain or anything. They cleared up that little detail after the fact, acquiring the name today, reports Fusible. The domain's original owner isn't saying anything about what convinced him to let go of it.
Yes, I'm assuming it was money, as opposed to a threat from a lawyer over a Microsoft trademark. That's because I don't know the law about such things, except that the law is kind of expensive and time consuming, so throwing a little dough at the owner is probably quicker and cheaper and doesn't buy them a one-way ticket to Bad PR Island.
Fusible caught up with the previous owner, a Scott O'Reilly of Rochester, Minn. O'Reilly said the only term of the agreement he can disclose is that he can't disclose any terms of the agreement. I hope O'Reilly said that in the form of a toast to Joseph Heller.
Fusible notes that Microsoft does not own halo.com or halo1.com, but does own halo2.com and halo3.com. It's unknown how long O'Reilly owned halo4.com, but my guess is a smart person would have registered it the day Halo 3 was announced. Good long-term investment.