UPDATE: All clear. The issues have been resolved, and servers should be operational once again.

Original Story: 

Activision has updated the status page for Call of Duty: Black Ops 2, Advanced Warfare, and Black Ops 3 to state that the servers are currently at DEFCON 1 with services offline. Many users are reporting connection issues.

Activision has stated that their operations team is aware and working on fixing the issue as soon as possible.

Server status pages: Black Ops 2, Advanced Warfare, Black Ops 3