A flood attack of an information system is simulated by injecting an algorithmically compressed flood attack model into the information system to assess the effect of the attack upon the system. The flood attack model propagates from node to node throughout the system by way of virtual messages that time-project the flood attack model and do not disrupt system operation while the simulated flood attack is taking place. Programs of executable code installed on nodes of the information system generate and send the virtual messages describing the flood attack.