Confidentiality (privacy) is the assets of preventing confession of information to illegal individuals or systems. For instance, a credit card transaction on the Internet requires the credit card number to be transmitted from the buyer to the merchant and from the merchant to a transaction processing network. The system effort to enforce privacy by enciphering the card number during broadcast, by preventive the places where it might appear (in databases, log files, backups, printed receipts, and so on), and by restricting access to the places where it is stored. If an illegal party obtains the card number in any way, a breach of privacy has occurred.
Breaches of privacy take many forms. Permitting somebody to look over your shoulder at your computer screen while you have private data present on it could be a breach of privately. If a laptop computer contain sensitive information about a company's employees is sold or stolen, it could result in a violate of privacy. Giving out confidential information over the telephone is a breach of confidentiality if the caller is not authorized to have the information.
Privacy is necessary (but not sufficient) for maintaining the privacy of the people whose personal information a system holds.