Bruce Schneier says Someone Is Learning How to Take Down the Internet:
Recently, some of the major companies that provide the basic infrastructure that makes the Internet work have seen an increase in DDoS attacks against them. Moreover, they have seen a certain profile of attacks. These attacks are significantly larger than the ones they're used to seeing. They last longer. They're more sophisticated. And they look like probing. One week, the attack would start at a particular level of attack and slowly ramp up before stopping. The next week, it would start at that higher point and continue. And so on, along those lines, as if the attacker were looking for the exact point of failure.
The attacks are also configured in such a way as to see what the company's total defenses are. There are many different ways to launch a DDoS attacks. The more attack vectors you employ simultaneously, the more different defenses the defender has to counter with. These companies are seeing more attacks using three or four different vectors. This means that the companies have to use everything they've got to defend themselves. They can't hold anything back. They're forced to demonstrate their defense capabilities for the attacker.
(Via Schneier on Security)