A Denial of Service (DoS) attack is a flood of packets that consumes network resources and causes gridlock. This gridlock prevents or denies users access to online resources, which is the origin of the term, "Denial of Service" attack. An attack may originate from a single source (DoS), or remotely from numerous machines (Distributed DoS or DDoS) that have been infiltrated. These pawn-like computers that forward DoS attacks are called "zombies", and are usually distributed geographically.