Game Rules Guide

You can delete your own messages in world, alliance and direct chat at any time, even if you are muted or the conversation is read-only. The message keeps its place in the conversation but shows "This message was deleted." instead of its text, and that is different from the notice shown when a moderator removes a message. Deleting a message cannot be undone. If someone is sitting your account, they can delete only the messages they sent themselves, and only while they may send.