Block repeat downloads by IP or account?

[Greebo]

We had a recent situation where a number of IPs were downloading the same attachment over and over again. While I believe some were legit (we had been referenced on a popular site), I also believe we got targeted by a DOS attempt, because the same file was being downloded in some cases by 0 post uers again, and again, and again. 27 Gigs in 2 days and we're a small forum with a 500G/mo limit.

I don't want to restrict guest attachment downloads completely - but I have for now, and am also forcing free email users to manually request access before getting permission to download attachments. But what I'd really like is a hack to restrict the amount of bandwidth a single IP and/or account can use. I'd like to restrict accounts from d/l the same attachment more than once every, oh, 5 minutes, and the same restriction on IP addresses.

Anyone know of any defensive hacks that would help with this?

Thanks much!
Chuck