Because a computer system must be accessible to authorized users, it must have portals of accessibility, and it is through these portals that the computer system becomes vulnerable to intrusion. Computer security is further complicated by the fact that only a fraction of the threat comes from outside the system. The approach to securing a computer system needs to be multi-faceted, one that has a competent authentication system for secured access, has an intrusion detection system to monitor system activities, and incorporates effective auditing procedures to assess the extent of a security breach and collect appropriate evidence. Products on the market to protect computer systems are briefly described, and the importance of proactive computer system protection is emphasized. 4 illustrations