A data breach is a security incident, that can lead to the destruction, loss, alteration, or unauthorized sharing of personal data. The causes of a data breach can be both accidental or deliberate, with malicious intentions.
You should note that a data protection breach isn’t only the loss of data. Examples of data breaches are also the access to the data by an unauthorized third party, the loss or theft of devices containing personal data, the alteration of personal data without permission, etc.
Therefore, data protection breaches can happen for the most various reasons, and it would be wrong to assume they’re always caused by external hackers.