I'm pretty sure the "Hacking attempt" error message is a misinterpreted one on the website's part, and I'm not entirely sure as to why it appears when some users try to change their signatures or other small things about their profiles.
I believe the forum might be misinterpreting the error message, perhaps if you were logged into both the golden box at the top of the forum, along with the login box below the forum banner. Sometimes it will act a little squirrely if this is the case.
I honestly don't think that you have much to worry about as far as hacking attempts go (so long as you have never been giving out your password to anyone in the game), but if do wish to change your password for security reasons as a "just in case," then that's perfectly understandable as well.
