  Computer infections such as viruses and worms spread over networks of
contacts between computers, with different types of networks being exploited by
different types of infections. Here we analyze the structures of several of
these networks, exploring their implications for modes of spread and the
control of infection. We argue that vaccination strategies that focus on a
limited number of network nodes, whether targeted or randomly chosen, are in
many cases unlikely to be effective. An alternative dynamic mechanism for the
control of contagion, called throttling, is introduced and argued to be
effective under a range of conditions.
