"[http://www.cert.org/tech_tips/denial_of_service.html Denial of service]" refers to attacks generated by aggressors that do not necessarily attempt to gain unauthorized access. They include "simple" denial of service, which usually exploits buggy code in the network implementation of the target, or wide disparity between the cracker's high bandwidth and the target's low, as well as [http://staff.washington.edu/dittrich/misc/ddos/ DDoS], which uses so called zombie daemons which are inserted on various compromised hosts and directed to spam the target with all available resources.