Just had a strange issue last night where an entire site went offline, it seems that somehow though all users to visit the site were being faced with the 'bad person' message from admin tools.
I disabled main.php by renaming, logged in, didnt see anything untoward, then turned back on main.php, and i was able to access again.
Now, this i put down to some kind of strange glitch, a one off, until it happened again today, on a totally different site, suddenly all visitors to the site are faced with this message.
I will need to investigate further to see if i can replicate the issue, however i wanted to post this to see if you had noticed anything similar and a possible fix.
I have a hunch that anytime an admin is blocked accessing query string wrong, then it might block all visitors instead of just a single IP block, i will test some more and report back too.