If it's in the db as numbers, then my guess would be the word censor. You can check by going to the "Word Censors" section of the administration panel. If it's not that and you haven't installed any MODs that might be doing it, I have no idea.
Issues with phpBB.com search
P.S. I tried to search the forum, but the search doesn't seem to be functioning.
You can also use google to search through the phpBB.com site by adding "site:www.phpbb.com
" after your query. For example: "cannot login site:www.phpbb.com