More from the article ...

... The security snafu was reported by Dutch regional broadcaster Omroep Gelderland. In a Thursday report, Omroep Gelderland journalist Just Vervaart said the broadcaster was able to track HNLMS Evertsen, a Dutch air-defense frigate deployed to help protect France's aircraft carrier Charles de Gaulle against missile threats, by mailing a Bluetooth tracker concealed in a postcard to the ship.

Per Vervaart, the Dutch Ministry of Defence makes it easy to send mail and packages to soldiers and sailors in the Dutch armed forces and posts full instructions online. It's that freely available open-source intelligence data that Vervaart was able to use to send the tracker to the Evertsen.

The report says the tracker remained active for about 24 hours, showing HNLMS Evertsen leaving port in Heraklion, Crete, and sailing first west along the island's coast before turning east toward Cyprus. The tracker finally went offline a day later when the ship was near Cyprus, and hasn't come back online. ...

... and kudos to the journalist who exposed this possible major breach of security.