In IT security terminology, firewall is defined as $$

Software or hardware device that controls access to a private network from a public network $($Internet$)$ by analyzing data packets entering or exiting it$.$

Probability of a threat exploiting a vulnerability and the resulting cost of the loss, damage, disruption or destruction risk is a function of threat, vulnerability and cost of impact.

The ability of an IS to continue to operate when a failure occurs, but usually for a limited time or at a reduced level.

$q,4)$ A program $($code$)$ that allows attackers to automatically break into a system through a vulnerability.