Under what condition must a controller notify the supervisory authority of a personal data breach?

The correct answer is based on the stipulations laid out in the General Data Protection Regulation (GDPR) regarding personal data breaches. A controller is required to notify the supervisory authority if a breach is likely to result in a risk to the rights and freedoms of natural persons. This means that the threshold for notifying the supervisory authority is not necessarily dependent on the breach being confirmed or on whether it occurred within the organization; rather, it centers around the potential impact on individuals' rights and freedoms.

This assessment of "risk" is critical because it recognizes that even potential breaches, which might not yet have confirmed adverse effects, could still pose significant threats to individuals. The emphasis here aligns with the GDPR's proactive approach to data protection, encouraging organizations to act swiftly when the possibility of harm exists.

The other options focus on different thresholds or conditions that do not align precisely with the GDPR requirements. For example, the notion of "high risk" establishes a stricter criterion that exceeds the general requirement of "risk," while confirmation of the breach alone or its location within an organization does not account for the necessary evaluation of potential impacts on rights and freedoms.