enigma1 - 11:57 am on May 15, 2012 (gmt 0)
In which way they abuse your site? Is it connections and b/w wasted or account/checkout problems? For instance, if you're using customer accounts for your cart, then one way is to force a validated account creation meaning the customer gets an email about his account registration and has to click a link to activate his account. If there is a vulnerability with your site then you should fix it. Look at the server logs to see what they try to access from the proxy your refer to.