Appearing at the INFOCOM conference in April 2003, this research paper provides insight into critical factors necessary to contain outbreaks of self-propagating code on the Internet. Citing the outbreak of the Code-Red worm in 2001 as an example, the authors justify the need for better methods of quickly controlling the spread of malicious code and minimizing damage. A couple scenarios for the deployment of a containment systems are identified, and their simulated effectiveness for dealing with a worm outbreak are discussed. The paper serves as a good starting point for anyone interested in learning about the technical issues associated with self-propagating code, and can also be useful for Internet security professionals who need to evaluate current containment systems or implement new ones.