I was editing a post today and noticed that under the drop down box for post author there was a name I never created and certainly didn't authorize - "WayneDantzler82." When I click on the tab for users that same name appears under Administrators except that it disappears after about half a second. Its like it is there but then quickly refreshes to remove the name. I noticed that this person is user #9 and while his name quickly disappears there is no user #9 listed (there is a user 8 and 10 so if I hadn't noticed the disappearing name I'd certainly see the skipped number.
I'm worried this is some hacker abusing my site. I don't see any new posts or changes to the site, but I'm freaking out over what might be done. Any suggestions or helpful advice? Since the name disappears under users I cannot actually delete the user.