Don't forget the first "D" in "DDoS." The Storm botnet, at its peak, had estimates between 1 and 10 million computers. Many, many more botnets have between 10

Don't forget the first "D" in "DDoS." The Storm botnet, at its peak, had estimates between 1 and 10 million computers. Many, many more botnets have between 100,000 and 1,000,000. It would be far easier to get ISPs to cooperate with a backscatter trace on one or a few computers spoofing random IPs than to track and shut down hundreds of thousands of computers.