After a decade of intensive investigation, peer-to-peer computing has established itself as an accepted research field in the general area of distributed systems. peer-to-peer computing can be seen as the democratization of computing-overthrowing the old regime of hierarchies as in client-server systems-largely brought about by last-mile network improvements which have made individual PCs first-class citizens in the computer world. Initially, much of the focus in peer-to-peer systems was on best-effort file sharing. However, over the last few years, research has also been directed at trying to make peer-to-peer systems satisfy properties and have functionality as exhibited by more traditional forms of distributed systems. Examples of such properties and functionality, which in principle run counter to the disorganized nature of peer-to-peer systems, are certain levels of security and providing reliable distributed storage such as required by databases.