The SEI helps advance software engineering principles and practices and serves as a national resource in software engineering, computer security, and process improvement. The SEI works closely with defense and government organizations, industry, and academia to continually improve software-intensive systems. Its core purpose is to help organizations improve their software engineering capabilities and develop or acquire the right software, defect free, within budget and on time, every time.
We estimate the number of active machines per hour infected with the Conficker-C worm, using a probability model of Conficker-C’s UDP P2P scanning behavior. For an observer with access to a proportion of monitored IPv4 space, we derive the distribution of the number of times a single infected host is observed scanning the monitored space, based on a study of the P2P protocol, and on network and behavioral variability by relative hour of the day. We use these distributional results in conjunction with the Levy form of the Central Limit Theorem to estimate the total number of active hosts in a single hour. We apply the model to observed data from Conficker-C scans sent over a 51-day period (March 5th through April 24th, 2009) to a large private network.