From a GDPR perspective, data breaches are our worst nightmare. By accessing our systems, hackers and the like gain access to personal data placed in our care; and the consequences can be dire.
Read the support notes
The two pages in your workbook, 11a and 11b, provide the means to log these breaches, if they ever occur, and the action you have taken thereafter.
Read the relevant support notes. All of the work you have done in completing your GDPR Workbook is aimed at minimising data breach and its consequences.
Pleased to say that thus far I have no breaches to report.