Was there a security breach at the top of government?

It is being reported that when Lis Truss was Foreign Secretary her phone was hacked:

Liz Truss phone hack claim prompts calls for investigation – BBC News

This hack was discovered when she was campaigning to be PM (she is now the record holder for the shortest Premiership in UK history) but it was covered up.

Your takeaway from this is – threat actors and cyber security incidents thrive when we keep information in the shadows.