Under the DPA 2017, a personal data breach is a breach of security leading to the accidental or unlawful destruction, loss, alteration, unauthorized disclosure of, or access to, personal data transmitted, stored or otherwise processed.

A controller must without undue delay and, where feasible, not later than 72 hours after having become aware of it, notify the personal data breach to the Commissioner. Where the Controller fails to notify the personal data breach within the 72 hours' time limit, he should provide the Commissioner with the reasons for the delay. Where a processor becomes aware of a personal data breach, he shall notify the controller without undue delay.

Where a personal data breach is likely to result in a high risk to the rights and freedoms of a data subject, the controller shall also communicate the personal data breach to the data subject without undue delay.

The communication of a personal data breach to the data subject shall not be required where:

• the controller has implemented appropriate technical and organisational protection measures, and those measures were applied to the personal data affected by the breach, in particular, those that render the data unintelligible to any person who is not authorised to access it, such as encryption;
• the controller has taken subsequent measures to ensure that the high risk to the rights and freedoms of the data subject referred above is no longer likely to materialise; or
• it would involve disproportionate effort and the controller has made a public communication or similar measure whereby data subject is informed in an equally effective manner.