&gt;If I run, say, a porn site, hosted in the US, as a US company, is it my responsibility to prevent users in a country where pornography is illegal from using my sit<p>Actually you have in most cases as trade agreements and various treaties usually provide the framework to extend laws and regulations between countries.<p>Gambling sites for example wether they are run from the UK, Malta or CAR explicitly block US users due to US laws which prevent online gambling.<p>If you are running a gambling site even in some 3rd world non extradition country if you do not respect the UIGEA you&#x27;ll be sanctioned and an arrest warrant will be issued faster than you can say poker stars.