install mod_iprot or something to limit the number of logins. put a threshhold of 3 /24's. once it gets to be more than that, close the account. case solved. you get to keep the dough from the carded/real-but-shared account, and you don't have to waste the bandwidth on the visitors anymore
one time a long long time ago i ran an xxx password site.. but it also did the favor of emailing the site owners as well to inform them a couple days after i listed the accounts.. one guy replied and said "i could care less.. the minute more than 3 people use the account it gets locked out anyway.. you're doing me a favor by exposing the hacked ones.."
so let technology control your site. setup something like that and "don't give a shit" about password spreading. hell, submit some of your own so people are tempted to buy your content once they get a quick taste before the account is closed