Answer yes if your organisation has a documented process for notifying the relevant Authority for your jurisdiction and all data controllers or other relevant parties when it becomes aware of a security breach involving Personal Data.
Under the GDPR, there are certain incidents that must be reported to the relevant Supervisory Authority (if you are in the UK, that's the ICO). All organisations that process personally identifiable information (PII) should have a process in place to assess a potential breach and to notify the relevant Authority if required.
A useful guide on what you must do after becoming aware of a potential breach was published by the ICO and can be found here.
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