Computer security - the protection of data and computer systems from intentional, malicious intervention - is attracting increasing attention. Much work has gone into development of tools to detect ongoing or already perpetrated attacks, but a key shortfall in current intrusion detection systems is the high number of false alarms they produce. This book analyzes the false alarm problem, then applies results from the field of information visualization to the problem of intrusion detection. Four different visualization approaches are presented, mainly applied to data from web server access logs.