ZoneAlarm is designed to protect your DSL- or cable-connected PC from hackers. This program includes four interlocking security services: a firewall, an application control, an Internet lock, and Zones. The firewall controls the door to your computer and allows only traffic you understand and initiate. The Internet lock blocks Internet traffic while your computer is unattended or while you’re not using the Internet, and it can be activated automatically with your computer’s screensaver or after a set period of inactivity.