Final answer:
Building Block should have first conducted a Data Protection Impact Assessment (DPIA) to identify risks, ensure a lawful basis for processing personal data, and provide transparency to individuals under GDPR before implementing a SecurityScan measure.
Step-by-step explanation:
To comply with the General Data Protection Regulation (GDPR), the first step Building Block should have taken before implementing the SecurityScan measure would be to conduct a Data Protection Impact Assessment (DPIA). This assessment is crucial in identifying and mitigating data protection risks associated with new projects or systems. The GDPR mandates a DPIA particularly for processing operations that are likely to result in a high risk to the rights and freedoms of individuals, which could include measures like SecurityScan that process a significant amount of personal data. Furthermore, Building Block should ensure that it has a lawful basis for processing the personal data, such as obtaining informed consent from the individuals whose data will be scanned, especially if sensitive data is involved. In addition, it would be necessary to provide clear information to those individuals about what data is being collected, how it is being processed, and for what purpose, in line with the GDPR's principles of transparency and accountability. It may also involve implementing safeguards and security measures to protect the data, adhering to the GDPR's principles of privacy by design and by default.