Cancer nodes
Malicious nodes. These may block specific keys, harvest nodes, flood the network, or otherwise be evil. These are the biggest internal security concern (obviously there are also external security concerns i.e. whether the network is invisible).
Cancer nodes on OpenNet may pretend to be a large number of real nodes. A classic attack against 0.5 is to create an UberNode which pretends to be many different nodes, and always resets the node reference on any successful request to one of its other aliases. This can then quickly get connected to every node on the network, and once it is, then we can have some fun! :)
