The companies that make our digital devices think – and act – like they still own them, even after we’ve bought them. Are we becoming digital serfs?

Internet-enabled devices are so common, and so vulnerable, that hackers recently broke into a casino through its fish tank. The tank had internet-connected sensors measuring its temperature and cleanliness. The hackers got into the fish tank’s sensors and then to the computer used to control them, and from there to other parts of the casino’s network. The intruders were able to copy 10 gigabytes of data to somewhere in Finland.

By gazing into this fish tank, we can see the problem with “internet of things” devices: We don’t really control them. And it’s not always clear who does – though often software designers and advertisers are involved.

In my recent book, “Owned: Property, Privacy and the New Digital Serfdom,” I discuss what it means that our environment is seeded with more sensors than ever before. Our fish tanks, smart televisionsinternet-enabled home thermostatsFitbits and smartphones constantly gather information about us and our environment. That information is valuable not just for us but for people who want to sell us things. They ensure that internet-enabled devices are programmed to be quite eager to share information.

Take, for example, Roomba, the adorable robotic vacuum cleaner. Since 2015, the high-end models have created maps of its users’ homes, to more efficiently navigate through them while cleaning. But as Reuters and Gizmodo reported recently, Roomba’s manufacturer, iRobotmay plan to share those maps of the layouts of people’s private homes with its commercial partners.

Read more: The ‘internet of things’ is sending us back to the Middle Ages