Airline systems are breached or subpoenaed. Manifests showing who flew on which flight, in which seat, with which passport, surface in places the passenger did not expect: a journalist's investigation that draws on leaked records, a court filing in a case unrelated to the passenger, a researcher's published dataset.

The information is not as restricted as travellers assume. Frequent-flyer accounts hold years of travel history that is accessible to any party who breaches the account. Loyalty partner relationships extend the same record to hotels and car rental firms. The aggregated travel pattern is a fuller picture than any single trip suggests.

What this argues for is care in how the account is held: a recovery setup that cannot be defeated cheaply, periodic deletion of older trip records where the service allows, and an awareness that the travel record is among the more revealing categories of information about a person of standing.

The first sensible step is to know what the record presently shows.