Denial of service (DoS) usually refers to an attack that attempts to make a computer resource unavailable to its intended users by flooding a network or server with requests and data. It can also simply refer to a resource, such as e-mail or a Web site, that is not functioning as usual. Often, the denial is accidental rather than a planned attack, resulting from too many legitimate requests. However, malicious DoS attacks are still prevalent against network devices, and a newer breed of DoS attack targeted specifically at applications is becoming more and more common.