  Cybersecurity is an issue of increasing concern since the events of September
11th. Many questions have been raised concerning the security of the Internet
and the rest of the US's information infrastructure. This paper begins to
examine the issue by analyzing the Internet's autonomous system (AS) map. Using
the AS map, malicious infections are simulated and different defense strategies
are considered in a cost benefit framework. The results show that protecting
the most connected nodes provides significant gains in security and that after
the small minority of most connected nodes are protected there are diminishing
returns for further protection. Although if parts of the small minority are not
protected, such as non-US networks, protection levels are significantly
decreased.
