Answer: A firewall is any of a number of security measures designed to prevent unauthorized access to a computer or computer network.

Firewalls can be of the hardware or software variety. In other words, a firewall can be a separate device, or can be a program that is installed on a computer. The most effective firewalls seem to be a combination of the two.

Firewalls act as a virtual barrier between a computer and the network it is connected to. Firewalls attempt to verify that data was requested by the user of the computer.

Bottom line: A firewall is a crucial line of defense.