In recent years, game theory has provided insights into the
behavior of distributed systems by modeling the players as utility-maximizing agents.
In particular, it has been shown that selfishness
causes many systems to perform in a globally suboptimal fashion.
Such systems are said to have a large price of anarchy. In
this article, we extend this field of research by allowing some
players to be malicious rather than selfish. What, we ask, is the
impact of malicious players on the system consisting of otherwise
selfish players? In particular, we introduce the price of
malice as a measure that captures how much the system's efficiency
degrades in the presence of malicious players, compared to a purely
selfish environment. As a specific example, we analyze the price of
malice of a game that models the containment of the spread of
viruses. In this game, each player or node can choose whether
to install antivirus software. Then, a virus starts from a random
node and recursively infects all neighboring nodes that are not
inoculated. We establish various results about this game. For
instance, we quantify how much the presence of malicious players can
deteriorate or---in case of highly risk-averse selfish
players---improve the social welfare of the distributed system.