One way to increase participation in a volunteer computing system is to provide individual compensation as an incentive for volunteers. This can take the form of electronic credits proportional to the amount of work that they do (some ideas about this are presented in ), or it can be in the form of a lottery, such the one used in distributed.net, where part of the $10,000 RC5 challenge prize money from RSA Systems was offered to the volunteer team whose computer actually found the key. Such lottery schemes not only require less money from the sponsor, but also encourage participation (i.e., the more one works, the bigger one's chances of winning are), and discourages cheating (i.e., pretending to do the work does not give one any chance of winning).
If we extend the idea of individual compensation to that of group trading of computing resources as commodities, we get a market system. Not only can users (or groups of users, such as companies) sell their computing resources, they can also buy the resources from others, or barter trade (like in the example in Sect.3.2). If reliable mechanisms for electronic currency, accounting, and brokering are developed, market systems promise a practical and productive use for volunteer computing technology. The SuperWeb group at UCSB is already actively pursuing this goal .
Forced and paid volunteer computing can be combined in contract-based systems: clients can be required by contract to volunteer their computers as (part of) their payment for goods or services received. For example, information providers such as search engines, news sites, and shareware sites, might require their users to run a Java applet in the background while they sit idle reading through an article, or downloading a file. Such terms can be represented as a two-sided contract that both sides should find acceptable. While it is actually possible to hide forced volunteer Java applets inside web pages, for example, most users will consider it ethically unacceptable. Sites that require users to volunteer must say so clearly, and allow the user to back-out if they do not agree to the terms. Some of these ideas are discussed in [17,18].
Some problems in anonymous paid volunteer systems are cheating (pretending to do work and getting paid for it), and spying. If Company A purchases computing power from Company B, a spy in B may read data from A's computation while he is doing it. For some classes of computations, encrypted computation techniques can be used to alleviate this problem.