I recently encountered a severe attack on two of my leaf servers from the named subject. A huge influx of traffic was closing any opening ports and the buffers were not closing them on time which was causing the delays and eventually a netsplit. He or She must have been connected via proxy server.

report him to his ISP. They will find the source even if it is on a proxy.

But they can't/won't do anything about it.

You'd be surprised how bored an ISP admin can get sometimes, you never know, they might do something.

I wouldn't be surprised at all. Over the years I have reported people for doing bad things on IRC and only the big ISPs ever co-operate because they are they only ones that can afford to lose a few customers. In fairness to ISPs generally, most reply to my correspondence stating that they will deal with the issue raised in accordance with their various corporate policies but the thing is, some ISPs don't even have an Acceptable Use Policy, instead they rely on Terms of Use and the law of the land to base their day to day decisions relating to complaints.

For the record Bigpond, Optus and Primus are very co-operative and when the evidence accompanying the email is substantial they have at times disconnected a user without a warning, in other cases issuing a warning and then disconnecting for a further breach; the rest (and not necessarily all for the wrong reasons) prefer to keep as many customers as they can get. Being a reseller of bandwidth is a game of very low fiscal margins. There is also the issue of the culprit complaining about being cut off to the Telecommunications Industry Ombudsman (in the case of an Australian based dispute) or similar statutory authority in other countries where relevant. ISPs don't need the grief that comes with having to reconnect a lamer because of bullying from the TIO or solicitors, etc.

Alkoholik: It is not always (and probably rarely) possible for a luser who connects with a proxy to be traced. In all but the most serious cases (eg: where a crime has been committed) it's not worth the bother and time trying.