EDIT: ALL SERVICES HAVE BEEN RESTORED.

The Xbox Live service appears to be back up and running according to the Xbox Live Status Page and we were able to sign in and chat with some friends at the posting of this article, Sony Playstation however is still down.

A hacker group seems to be taking responsibility for this DOS Attack, but both companies have not issued an official statement just yet.

@AskPlayStation
Our engineers are continuing to work hard to resolve the network issues users have experienced today. Thanks for your continued patience!

@XboxSupport
Some Xbox One users may currently be experiencing issues signing into Xbox Live. Please see http://xbx.lv/XBLstus for more info. ^AD