The probability of ruin plays a crucial role in determining the network security risk. The stable rate, initial stable values, together with ruin time, ruin function will be discussed in the directions of mapping to the security systems. As the stable rate becomes larger, the observation is the probability of ruin will be smaller. Random walk, Brownian motion and the connection with network security risk also will be addressed. People can use the model to determine the implementation structure of the network security systems to prevent intrusions.