Cyber Crime: A simple yet sturdy definition of cyber crime would be "unlawful acts wherein the computer is either a tool or a target or both".
Where the computer is a tool for an unlawful act:
This kind of activity usually involves a modification of a conventional crime by using computers. Some examples are:
Sale of illegal articles
Intellectual Property crimes
Where the computer is the target for an unlawful act:
It may be noted that in these activities the computer may also be a tool. This kind of activity usually involves sophisticated crimes usually out of the purview of conventional criminal law. Some examples are:
Unauthorized access to computer systems or networks
E-Mail bombing:Email bombing refers to sending a large amount of e-mails to the victim resulting in interruption in the victims’ e-mail account or mail servers.
Data diddling:This kind of an attack involves altering the raw data just before it is processed by a computer and then changing it back after the processing is completed.
Salami attacks:Those attacks are used for the commission of financial crimes. The key here is to make the alteration so insignificant that in a single case it would go completely unnoticed e.g. A bank employee inserts a program into bank’s servers, that deducts a small amount from the account of every customer
Denial of Service: This involves flooding computer resources with more requests than it can handle. This causes the resources to crash thereby denying authorized users the service offered by the resources.
Data diddling:changing data prior or during input into a computer
Even without involving other people, it is possible to categorise certain action as cyber crime. A simple message encouraging terrorism or any unlawful activity, even if indirectly, would amount to cyber crime. It all depends upon the content of the writing on your account.