ReverseDOS - spam filter for ASP.NET sites

ReverseDOS is a very simple HttpModule that checks various parts of incoming requests against a list of crap that you don't want pushed on to your site. If ReverseDOS detects a match, it attempts to stall the requesting client for a number of seconds (specified in a .config file). During this loop, which uses virtually no server resources - and only a tiny smidgen of bandwidth, ReverseDOS checks every .3 seconds to see if the client is still connected. If the spammer disconnects, good riddance. If the spammer sticks around, they're finally rewarded with the Response Headers - containing an HTTP 403 - Access Denied Response Code. (Awwwhh tooo bad...)

http://www.angrypets.com/tools/rdos/