Which of the following best defines a 'data breach'?

A 'data breach' is best defined as accessing data without authorization. This situation occurs when an individual or entity gains access to sensitive or confidential information without permission, potentially exposing that data to unauthorized users. Data breaches can lead to the loss of personal information, financial data, or proprietary business information, and they often result in significant risks such as identity theft or corporate espionage.

In contrast, the other options do not fit the definition of a data breach. Encrypting data for safety is a protective measure taken to secure information and prevent unauthorized access. Sharing data among partners can be perfectly legitimate and typically occurs under agreed terms that protect the data, as long as it is done within legal and contractual frameworks. Regularly backing up data is also a good security practice that helps mitigate the impact of data breaches, but it does not involve unauthorized access to information. Therefore, option A accurately captures the essence of what constitutes a data breach.