Ubisoft Support team has acknowledged on Twitter that server issues are currently impacting a large number of Ubisoft games across all platforms.

We are aware of server issues impacting multiple games. Our technical team is investigating and working on resolving this as quickly as possible. We appreciate your patience and we will continue to update this thread as new information becomes available: https://t.co/myd5dDcFLh
? Ubisoft Support (@UbisoftSupport) January 6, 2018

As of this writing, we’re having trouble accessing official forums. The developer has noted that the outage may affect its websites and other online services as well . However, Ubisoft’s tech support site seems to be working, a post on which provides the following list of titles currently affected:
Anno 2205

Assassin’s Creed IV: Black Flag

Assassin’s Creed: Initiates

Assassin’s Creed: Ezio Collection
Assassin’s Creed: Rogue

Assassin’s Creed: Syndicate

Assassin’s Creed: Unity

Boggle

Child of Light

Far Cry 4

For Honor

Grow Home

Grow Up

Just Dance 2014

Just Dance 2015

Just Dance 2016

Just Dance: Disney Party 2

Just Sing

Monopoly Deal

Rabbids Crazy Rush

Rabbids Invasion

Rocksmith 2014

SCOM

Shape Playtime

Tetris Ultimate

The Crew

Tom Clancy’s The Division

Tom Clancy’s Rainbow Six: Siege

Tom Clancy’s Ghost Recon Wildlands

Toy Soldiers War Chest

Trials Frontier

Trials: Blood Dragon

UNO

Watch Dogs
Ubisoft says p...