UBB.threads PHP Forum Software Community Forums Resources and Customizing Admin Zone Ukraine bad requests

Since November, I'd had some "bad guys" hit my server with a weird request. Over the past 3 months I've banned them in my htaccess file and it seems to work... But as you know, the hits never stop.

Does anyone recognize this (from Ukraine) or have an idea how to protect against it? This morning it stopped my server for about an hour.

FOLLOWUP: Basically they enter the url of my Forum ending with ubbthreads.php and then they add about 30 or 40 "+'s" to it.... eg. ubbthread.php++++++++++++++++++++
and some other characters...

Is this a known way to overflow the buffer or cache or ????

Thanks.