Most countries would define "working" as earning money from an employer within that country itself, hence depriving citizens of that country of a prospective job.
That's wrong. I know from big corps that employees always have to ask for work permission when going to the US (or other countries) for things like development, even for one week. For most countries in the world you actually need a work permission to do that. Single exception is when you do customers meetings all the time and have a secretary typing for you.
Except no one can verify what you do exactly. You always tell the immigration officer at the airport (if he/she asks you) that you're visiting for "meetings". But who does meetings 9-5 every day for 2-3 weeks?
Basically you're OK as long as you don't get paid for your work there. My friend works in the oil/gas industry and he keeps flying to different countries frequently and works there for almost 3-4 weeks. But he doesn't get paid in that country (he gets some per-diem allowance but that's all).
