  A distributed denial-of-service (DDoS) attack is an attack wherein multiple
compromised computer systems flood the bandwidth and/or resources of a target,
such as a server, website or other network resource, and cause a denial of
service for users of the targeted resource. The flood of incoming messages,
connection requests or malformed packets to the target system forces it to slow
down or even crash and shut down, thereby denying service to legitimate users
or systems. This paper presents a literature review of DDoS attacks and the
common defense mechanisms available. It also presents a literature review of
the defenses for low-rate DDoS attacks that have not been handled effectively
hitherto.
