Answer: Distributed Denial of Service attack.

A DDOS attack is the next generation of a DOS attack. Years ago, you could attack a server or website from 1 single host (computer). For example: the ping of death. By ping'ing a web server (or any internet based server) repeatably, the server has to respond thereby using precious CPU cycles. The ping of death would lock up an internet server causing other requests to that server to be denied. A DDOS is the same concept but instead of the attack coming from one computer, it is coming from multiple computers (or hosts). Hence, the attack is distributed.

Makers of firewalls caught on which is why today any firewall admin worth his salt will turn off responding to any ICMP request (ping, trace route) so the server behind the firewall will never receive the ping.

Normall, it is just one company that is attacked. I don't believe I've heard of an intire ISP being attacked. I would hope they have decent security with the knowledge to implement and maintain it.