"They are appliances in that they are easy to use, while not easy to tinker with," he writes. "They are tethered because it is easy to for their vendors to change them from afar, long after the devices have left warehouses and showrooms."
They are a world away from the "generative Internet", a term Zittrain uses to describe the open, creative, innovative approach that helped build the Internet.
The rise of viruses and fraud has also led to tighter controls on PCs, particularly those in schools, universities, offices and public places, Zittrain says.
People are often blocked from experimenting with shared computers and their input is severely limited.
There is still time to save the Internet, he believes, although the answer lies in social rather than technological changes.
Society should resist more regulation and place its trust in the Internet's users. The success of Wikipedia, the online encyclopaedia written and edited by its readers, shows how self-governance can work.
Internet users should see themselves as "netizens", active participants in the online world rather than passive consumers.
"The community itself exercises a form of self-restraint and policing," he said. "You see it in Britain when you try to jump a queue, you see it on Wikipedia when a page is vandalised.
"The challenge to the technologists is to build technologies to let people of good faith help without having to devote their lives to it."
* The Future of the Internet and How To Stop It, futureoftheinternet.org , is published by Penguin.