This article investigates selfish behavior in games where players are
embedded in a social context. A framework is presented which allows us to
measure the Windfall of Friendship, i.e., how much players benefit (compared to
purely selfish environments) if they care about the welfare of their friends in
the social network graph. As a case study, a virus inoculation game is
examined. We analyze the corresponding Nash equilibria and show that the
Windfall of Friendship can never be negative.