brute force crack help

[J-DAM]

I run a few sites, and for the first time ever, some punkass is running a brute force crack attempt on one of the sites. He's already racked up 6 million attempts and counting, and its wrecking havoc on my bandwidth. I actually had to disable the members area, because it was getting ugly.

Do any of you computer people know a way to thwart the attempts of these dastardly rapscallions? Any insight you can provide is welcomed. Thanks.