Denial of Service (DoS) is an attack on a computer or network that prevents legitimate use of its resources. In a DoS attack, attackers flood a victim system with non-legitimate service requests or traffic to overload its resources, which prevents it from performing intended tasks.

Which of the following is a symptom of a DoS attack?
Unavailability of a particular website
Decrease in the amount of spam emails received
Automatic increase in network bandwidth
Automatic increase in network performance