DDOS -- hitting all the federated servers with bogus transactions/packets
P2P -- Pretending to be a real peer in the peer 2 peer network but generating false info
BGIP -- Attacking the network infrastructure directly (overflow attacks, BGIP specific DDOS attacks) -- this is mostly an issue if the federated servers are on the same network/cloud platform
These are the ones I can think of off hand. Robert, do you have more context? I would suggest this task next be assigned to Brian for input.
Create list of attack vectors that Factom will be subject to, to aid in testing