In this paper we present the Behaviosite paradigm, a new approach to affecting the behavior of distributed agents in a multiagent system, which is inspired by biological parasites with behavior manipulation properties. Behaviosites are special kinds of agents that "infect" a system composed of agents operating in that environment. The behaviosites facilitate behavioral changes in agents to achieve altered, potentially improved, performance of the overall system. Behaviosites need to be designed so that they are intimately familiar with the internal workings of the environment and of the agents operating within it, and behaviosites apply this knowledge for their manipulation, using various infection and manipulation strategies. To demonstrate and test this paradigm, we implemented a version of the El Farol problem, where agents want to go to a bar of limited capacity, and cannot use communication to coordinate their activity. Several solutions to this problem exist, but most yield near-zero utility for the agents. We added behaviosites to the El Farol problem, which manipulate the decision making process of some of the agents by making them believe that bar capacity is lower than it really is. We show that behaviosites overcome the learning ability of the agents, and increase social utility and social fairness significantly, with little actual damage to the overall system, and none to the agents.