A news announcement on the login screen is letting us all know that AT&T, the people who provide data center service to Blizzard, will be performing maintenance tonight from 12:00 a.m. EST until 5:00 a.m. EST.

This will likely cause problems with both being able to login to the game and stay connected. This is an odd maintenance announcement, and one that I don't recall seeing before.

Hopefully this will not develop into anything more serious – such as extended network outages or other such issues.