The prohibition against work on tourist visas makes sense when work is defined as it was historically (being hired by a company in the country that otherwise would have hired a citizen)...
Few laws say what is legal they normally say what is not. I would imagine few countries specifically say it is legal to do work from another country (as a digital nomad, as a employee answering an email on your vacation, as a private investor reading the news and using the internet to buy or sell a stock using your broker at home, as a writer writing your book that will be published back home or whatever). It seems pretty obvious you are not blocked from answering a work email while on vacation but exactly at what point a country wants to draw a line on acceptable work on a tourist visa and unacceptable work is not easy.
continue reading: Economics: Digital Nomads, Visas, Foreign Currency