In a recent alert from Prolexic Technologies they have uncovered a new type of dDoS attack. This attack uses p2p networks to perform the attack. This is very much different from a BotNet attack. see below
P2P attacks are different from regular botnet. There is no botnet and the attacker doesnt have to communicate with the clients it subverts. Instead, the attacker acts as a puppet master, instructing clients of large P2P file sharing hubs to disconnect from their P2P network and to connect to the victims website instead. As a result, 25k computers may aggressively try to connect to a target website.
Here is what they have to say about the solution:
Plugging up web servers isnt anything new, but the ability to block 150k+ attacking IP addresses is. While dc++ attacks are easy to identify with signatures, the large number of IP addresses that need to be blocked (often over 250k during the course of a big attack) means that this type of attack can overwhelm even functioning intrusion prevention systems (IPS).
