Earlier today, certain realms were affected by an in-game exploit, resulting in the deaths of player characters and non-player characters in some of the major cities. This exploit has already been hotfixed, so it should not be repeatable. It's safe to continue playing and adventuring in major cities and elsewhere in Azeroth.
As with any exploit, we are taking this disruptive action very seriously and conducting a thorough investigation. If you have information relating to this incident, please email firstname.lastname@example.org. We apologize for the inconvenience some of you experienced as a result of this and appreciate your understanding.