T-Mobile USA is going after data thieves, which it says are taking advantage of the company's unlimited high-speed data plan through excessive tethering - the use of smartphone data service on other devices.

The carrier offers unlimited 4G LTE on smartphones, but limits data usage through tethering to 7GB a month under a Smartphone Mobile HotSpot feature, which reduces speed beyond that limit. If a customer needs more LTE tethering, they can add on more.

But CEO John Legere late Sunday accused some users of “hacking” the system to swipe high-speed tethered data, by strategies like downloading apps that hide their tether usage, rooting their phones, or writing code to mask their activity.

"It’s a small group – 1/100 of a percent of our 59 million customers – but some of them are using as much as 2 terabytes (2,000GB!) of data in a month," Legere wrote.

"I’m not sure what they are doing with it – stealing wireless access for their entire business, powering a small cloud service, providing broadband to a small city, mining for bitcoin -- but I really don’t care!," he added.

Legere said the company was going first from Monday after the 3,000 users who know exactly what they are doing, as they can compromise the network experience for other T-Mobile customers. The company claims to have developed technology that can detect the people who choose to break its terms and conditions.

Erring customers will be warned, and then lose access to the company's unlimited 4G LTE smartphone data plan, and be moved to an entry-level limited 4G LTE data plan, according to a support page.