Thousands of broadband internet modems are being installed with default passwords, making them vulnerable to hackers who can use them to surf the net at the owners' expense.

But when Auckland computer programmer John Burns tried to warn people that their modems were insecure, he was threatened with legal action.

Burns said he bought a Nokia M1122 modem/router a month ago when he subscribed to Telecom Jetstream fast internet account.

"About a week after I started, I checked the logs on the modem and discovered some configuration settings had been changed," Burns said.

Extra mapped ports or "pinholes" had been added, linking the router to overseas servers.

"Someone was using my router as a stepping-stone for the transfer of data."

New Zealand Herald