Acknowledgments

We thank the anonymous USITS reviewers for helping us improve this paper. This research was sponsored by DARPA agreements F30602-99-1-0157 and N66001-00-1-8920; by NSF grants CAREER:CCR-9876128 and CCR-9988176; and Microsoft. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright annotation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as representing the official policies or endorsements, either expressed or implied, of DARPA, Rome Labs, SPAWAR SYSCEN, or the U.S. Government.