On October19,1997, distributed.net, a world-wide computing network composed of thousands of volunteer machines, successfully cracked the RSA Systems RC5-56 code challenge . This network achieved an average aggregate computing power equivalent to about 26,000 commodity PCs, and involved as many as 500,000 different computers (as distinguished by their IP addresses) over a span of 250 days .
A large part of this success can be attributed to the relative ease with which users are able to join distributed.net. To volunteer, a user only needs to:
While this approach to volunteer computing has clearly proven its worth, it still has its limitations. First, volunteers still need some technical knowledge - at least enough to download, install, and run the software. Furthermore, a non-trivial amount of programmer effort is still required to write, compile, and test code for all the possible target architectures. In fact, this step may even be harder with distributed.net than with PVM because there might not exist a standardized cross-platform library for doing low-level operations, such as communications, and synchronization, that are already provided by PVM,
Perhaps the biggest problem with systems like distributed.net, however, is security. Although distributed.net, unlike PVM, does not require volunteers to give explicit remote shell access to anyone, it does require them to run programs which implicitly provide the same kind of remote-shell-like access anyway. The code which a volunteer user downloads is executed with user permissions, which means it can access any of its user's files and data, including sensitive data such as credit card numbers and passwords. Clearly, such a serious security risk would (and should) make people wary of volunteering, and thus poses a major obstacle in achieving volunteer computing networks of larger sizes.