In XCOM 2 , the aliens have won. They’ve occupied Earth and your team is attempting to defeat them and take things back. The thing is, some humans are okay with the aliens. They’re called Advent and they’re out to sabotage your endeavors with Dark Events.
If an Advent Dark Event is underway in XCOM 2 , you want to do everything possible to make sure it doesn’t happen. If the aliens’ human allies manage to carry out one of their missions, it has an effect on the rest of your game. Some of the Dark Events revealed so far include Hunt XCOM, which sends a UFO after the Avenger, Alloy Padding, which improves the armor of Advent soldiers on missions, Alien Cypher, which encrypts transmissions and makes intel more expensive for a month, and Rapid Defense, which brings in extra support on Guerilla Ops.
It also appears that only a few Dark Events will be immediately available to XCOM 2 players each round. Intel points will have to be expended to reveal all of them. Since some can hide extra Faceless on missions, you may want to do as much investigating as possible.
XCOM 2 is going to come to Windows, Mac, and Linux PCs in February 2016. Hopefully it will show up on consoles as well.
Source: XCOM 2