In this paper

propagation pattern of reactive worms is studied.The propagation model and the immunization model of reactive worms are proposed

in which dynamic factors of P2P networks are taken into account.Further

the sufficient condition of worms not attaining an endemic state is deduced from the model of propagation of reactive worms in applying Epidemiology.Large scale simulation experiments validate the models and the sufficient condition.All the simulations also show that among all P2P-related parameters

the downloading rate is the crucial factor to the propagation of reactive worms

the basic reproduction number of worms is the index of propagation capability of worms

and the sufficient condition is helpful to early warn the presence of an epidemic.In addition

by using data from the Gnutella network

the propagation capability

propagation speed and the risk of reactive worms are predicted and evaluated based on the propagation model.Prediction and evaluation show that it is time that reactive worms should be taken into account.