Because the P2P overlay is an self-organizing system, there are good
or bad intermediate peers between the source peer and the destination
peer. These intermediate peers may discard messages, misroute
messages,
do replay attacks, and etc. Or some peers can put victim's contact
information under popular resource to cause DoS attacks,
or manufacture a chosen-ID attack, and so many. I do think some of
these
attacks are very bad to the p2p overlay. I do believe the 'basic'
protocol
should provide the 'basic' defense for some general attacks, but not
for all
important attacks.