Have I been hacked?

  • So I had someone create a user account and created a thread and post in my forums. Although the post wasn't an issue, this individual seems to have been able to create a footer/signature area on the bottom of his post with a hyperlink to a site he's promoting.

    Now what ever he did, I cannot edit the post to delete this because the post HTML seems to end and the smiley. I've checked my settings in the ACP to see if I've allowed something I shouldn't have and don't see anything at first look. I'm sure deleting the thread will likely fix the situation but I'm more interested in how this user was able to achieve this to begin with. Is this a straight up hack or did I configure something wrong to allow this?

    Here's another pic showing the HTML for the link and footer he added.