Author: mcdevitd
Description:
Account names with double underscores persist in Special:ListUsers, even though clicking on them will tell you the account doesn't exist. As a result, they can't be blocked, or hidden from the list with HideUser. See the URL for an example from en.wp
Version: unspecified
Severity: normal
URL: http://en.wikipedia.org/w/index.php?title=Special%3AListUsers&username=Exclamation+mark+_&group=&limit=10