Thus, ddYl < 0. Similarly we can show that ddZl > 0. These conditions imply that equilibrium number of infected nodes decreases but protected node increases as the growth rate of antivirus software increases (see Figs. 4 and 8).
Further it can be shown that dKdY < 0 and dKdZ > 0. These conditions imply that in presence of a protected class, the cleaning process of infected network becomes accelerated by antivirus program as Y decreases and Z increases as K increases.