Blizzard's main page has been updated, so while you're waiting for the patch to download, read what they have to say:
Azeroth is under attack! Horrific creatures are swarming from a suddenly active Dark Portal and have rampaged into the Blasted Lands. Defenders from Nethergarde Keep have scrambled to meet the enemy head-on. However, even with the assistance of reinforcements from the ever-vigilant Argent Dawn, the forces of Azeroth need your help!
Not much is known of the invasion at this early stage, but early reports from the battlefront describe wave after wave of demonic attackers charging from the Dark Portal. It is also reported that Lord Kazzak was seen departing through the Dark Portal. In his stead he has left his minion, Highlord Kruul, to sow fear and confusion among the defenders.
Accompanied by a host of infernals, Kruul has been seen near a number of major cities in Azeroth, along with the following outdoor areas:
* Eastern Plaguelands
* Stranglethorn Vale
* Searing Gorge
Not even the elite forces of the Argent Dawn have dared attack Kruul directly. Only a large and well-coordinated group of adventurers might stand a chance of defeating him.
[Thanks to "rogue" for the submission!]