sss,
They will only be interested in scanning your network or trying to compromise your equipment if you put out an open invitation to them. I personally see absolutely no need whatsoever to have any services open on your ADSL interface. It's for surfing, not for serving.
My internet interface is absolutely, completely air-tight firewalled off. Nothing gets in, full stop. I allow pings so that the ISP and other people can verify that I am on and I allow the bare minimum ICMP packets so that important IP error messages make it through, but that is it.
Even the most hard up script kiddies will usually give up on scanning you if they have found nothing after about half a minute. If your firewall is blasting everything to oblivion, there will be no response to any of their scanning attempts and they will think you're probably dead in the water.
I log for scans, but have seen very little that actually interests me, in fact, I normally don't even check those logs, since I don't consider scanning to be an attack. People only offend me once they start trying to connect to things or blasting me with endless packets in a true script kiddy style DDoS attack.
At the moment, Telkom's counter has me at 765MB total throughput for the month. My own count is 767MB, I can't account for the discrepancy, but I'm guessting some traffic passing through my FreeBSD box doesn't reach the PPPoE server and isn't counted.
Of the 767MB I have counted, I have tried to calculate the amount of traffic caused by scans. So far, for the month, scanning has cost me the amount of 23KB of traffic. Seriously sss, if you are so greedy that you are going to go ape **** about a few kilobytes per month, you should be using pre-paid dial-up access with the smallest time voucher.
Instead of incessantly moaning about the problem, install a proper firewall to protect you from scanning and the attacks that might follow if you are found to be a soft target. If you don't know how to do this or don't want to do it because you are lazy, like most people, hire somebody who knows how to do it for you and I can guarantee you'll have seen the last of the script kiddies.
Willie Viljoen
Web Developer
Adaptive Web Development