A CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart) is a type of challenge-response system designed to differentiate humans from robotic software programs.
A denial-of-service attack is a security event that occurs when an attacker prevents legitimate users from accessing specific computer systems, devices, services or other IT resources.
A distributed denial-of-service (DDoS) attack is an attack in which multiple compromised computer systems attack a target, such as a server, website or other network resource, and cause a denial of service for users of the targeted resource.
The Electrohippies Collective is an international group of hacktivists based in Oxfordshire, England, whose purpose is to express its displeasure with the use of the Internet "as a tool for corporate communications and propaganda.
On the Internet, jolt is a denial of service (DoS) attack caused by a very large ICMP packet that is fragmented in such a way that the targeted machine is unable to reassemble it for use.
On the Internet, a packet monkey is someone (see cracker, hacker, and script kiddy) who intentionally inundates a Web site or network with data packets, resulting in a denial-of-service situation for users of the attacked site or network.
SYN flooding is a method that the user of a hostile client program can use to conduct a denial-of-service (DoS) attack on a computer server.