title: How Distributed Hash Table in IPFS and Bittorrent prevent abuse?
body: <p>My understanding is that IPFS and Bittorrent Mainline DHT are built on top of a Distributed hash Table (Kademlia).
  They use the file hash as Kademlia key to find a list of peer that might have this file.</p>
  
  <p>1- What I don't understand is if this is all decentralized who remove from the DHT peer that no longer host a file content?</p>
  
  <p>2- What prevent someone from storing large amount of data for free inside the DHT?</p>
  
  <p>3- What prevent someone from disrupting the network by adding large number of invalid peer for a popular file.</p>
  
  <p>4- What prevent a bad actor from joining the DHT ring and not following the routing protocol thus preventing discovery message from reaching correct nodes.</p>