An important development to keep a network clean from pseudospoofing (“Sybil”) and malicious attacks is a way to detect and blacklist unreliable or malicious storage nodes
An unreliable storage node is defined as a node that says it's storing data, but it isn't.
Those parts of files that it's receiving, are lost.
To prevent use of unreliable storage nodes, each client will check file integrity to be sure files are accessible.
Client keeps a relation of parts uploaded to each node. When a storage node where file were allocated there, is not giving the file, or answers that it doesn't have your file or is not online, after few retries in different days this node is marked as unreliable.
Each client will have a list of what it detected as an unreliable storage node.
Those list can be done in the introducer, too. In this way, introducer would prevent to notice about an unreliable storage node to possible clients.