This is effectively the law in nearly every country, but nobody gives a damn and it's impossible to track anyway. If there's no local company setup and no remittance of funds into the country, there's effectively no proof to go by. What are the authorities going to do, go to every coffee shop, seize every laptop, demand every password, and audit every email & web log? That's really what it would it require. Well guess what, the first country to become hostile to digital nomads like that will be writing its tourism death sentence.

There are countless thousands of digital nomads making a living online and working all over the world. To register for taxation in any country they're temporarily residing in would be insane (not to mention illegal under a tourist visa, yet there is no 'works online from a laptop' visa available anywhere yet). Thailand, which has become one of the largest digital nomad havens on the planet, is at least ahead of the game and working on a new visa category for online foreign workers (along with tax registration).

But seriously, with all of the gigantic problems/frauds going on (1MBD, FELDA, etc) a bunch of foreigners on laptops, contributing to the country via their spending, is really an issue to be this concerned about?