What is unauthorised access to computer systems and how can this type of computer crime affect a business.?

Concept: The entry of a user into a system that he does not have permission to use. A user gained access to another user's system. Access can be access to information as well as the power to send commands to maliciously change the system.

Effect: Case sensitive information is now freely available to anyone, and can be used for fraud like insider trading. Blackmailing can also take place. Information can be altered to portray biased information, and systems can be crashed by the planting of viruses and worms, in order to sabotage a company.