The basic definition of cyberterrorism

Cyberterrorism is the leveraging of a target's computers and information , particularly via the Internet, to cause physical, real-world harm or severe disruption of infrastructure.

Cyberterrorism is defined as “The premeditated use of disruptive activities, or the threat thereof, against computers and/or networks, with the intention to cause harm or further social, ideological, religious, political or similar objectives. Or to intimidate any person in furtherance of such objectives.” This definition was created by Kevin G. Coleman of the Technolytics Institute.^[1]

...subsumed over time to encompass such things as simply defacing a web site or server, or attacking non-critical systems, resulting in the term becoming less useful...

There are some that say cyberterrorism does not exist and is really a matter of hacking or information warfare. They disagree with labeling it terrorism because of the unlikelihood of the creation of fear, significant physical harm, or death in a population using electronic means, considering current attack and protective technologies.

The National Conference of State Legislatures (NCSL), a bipartisan organization of legislators and their staff created to help policymakers of all 50 states address vital issues such as those affecting the economy or homeland security by providing them with a forum for exchanging ideas, sharing research and obtaining technical assistance [1] defines cyberterrorism as follows:

the use of information technology by terrorist groups and individuals to further their agenda. This can include use of information technology to organize and execute attacks against networks, computer systems and telecommunications infrastructures, or for exchanging information or making threats electronically. Examples are hacking into computer systems, introducing viruses to vulnerable networks, web site defacing, Denial-of-service attacks, or terroristic threats made via electronic communication.[2] Demitri Jesus Olmo.(FROM:wikipedia the free encyclopedia)