You are taxable with your world income if you spend more than 180 days in the country by a rate of 35%. Of course most people never declare any income tax, bacuse they do not know what that is or they believe they are to poor to pay tax anyhow.
Adult Webmasters live dangerous as this example of a Filpino porn blogger/forum owner shows:
http://www.gmanews.tv/story/59587/(U...s-boybastoscom
The guy was pretty stupid by A) using his real name and address in the whois info, B) changing his whois info to the name of a konservative senate member who wants to run for president and C) subscribing to many adult websites, stealing their content and making it available for free on his forum.
If someone is smarter than him - and many are!!! - you could get away with shit pretty easily.