Hi, that was me. It wasn't because of spammers, but because of queries generated by the board.
This was what caused the last offline time of the board and I am trying to preventing this from happening again. that said I applied several query optimizations, and this was one of them.
I'll lower it to 7 seconds and see how it goes.
Ps: I am also thinking of changing the search engine to google, but before that I will probably move to a new host...
edit: queries = total queries per hour or queries within a short period of time