A couple of years ago, I chaired a discussion of cyber security managers from some well-known companies. How did they guard against a hack attack? One strategy mentioned was to track each department's comings and goings.

High staff turnover was a warning that the company's computer systems could be breached, they said. Being hacked required not only a malevolent external agent, but frequently an internal weakness too. That could be in-house sabotage; more often it was carelessness or inattention.

Staff departures could indicate low morale. At the very least, losing people who knew what they were doing and having