A pulsing zombie is a computer whose security has been compromised without its owner's knowledge by a cracker so that it intermittently carries out a denial-of-service attack on target computers in a network. Unlike a regular zombie, the pulsing zombie doesn't completely paralyze its targets, but merely weakens them, in what some call degradation-of-service attacks.
Whereas the usual zombie attack consists of a steady (and therefore more easily traced) stream of attack traffic intended to overwhelm one or more target computers, the pulsing zombie attack consists of irregular bursts of traffic intended to hamper service. It is more difficult to locate the source of an attack from a pulsing zombie, or even to know that an attack has taken place. Pulsing zombie attacks have been known to go on for months before they are detected; in one case, a victim received six times its normal traffic volume for several months, according to Asta Networks CEO Joe Devich.