We have a handful of places that we do not accept orders from. Often this includes places like Thailand, Nigeria and several other high-risk countries. The person from those countries never even get to our website/order pages as the countries are blocked in IP Tables to start with. If they use a proxy, that raises a red flag on our end too in the manual verification process.
There's also a number of countries that we (as a US Business) are prohibited from doing business with due to the US Treasury Embargo Restrictions. Some of those countries include Sudan, Syria, Cuba, Iran, North Korea, etc etc. For a list of counties prohibited by the US Treasury, check out - http://www.treasury.gov/resource-cen.../Programs.aspx
There are exceptions to the sanctions, but it requires government approval and extra paperwork.