I add one more note to all the responds It totally depend on your country and the country which host your site Some country's they do not take it serious but some others do. We talked about the nulled scipt where we can find them? in some specialized websites! If they supposed to shout first they need to be shout down but as all we can see they still working because in where which they located there is no strong law another issue is if your site is small they wont come after you because it wil cost them more! as you can see Microsoft usually will never come against home users who use it OS illegally As an example check en.wikipedia.org/wiki/Demonoid anyway stay safe ether use opensource SMF (which is the same useless) or buy the license. smf is not bad but i hate it because the force you to keep their long footer copyright as is! But i LOVE joomla that allow you to remove it completely (but i wont!!!!!!Because They gave me freedom and i respect them as well)
It depends on your country. The country you host in will only effect what actions they can take against you. If you host in a country that does not respond to takedown notices, they can still sue you. If you live in that same country, it is not likely. If you live in the US they might. vBulletin has gone after a number of small sites. It costs them nothing to send a takedown or C&D to the host as they have a legal team that they pay for whether those letters get sent out or not. It only costs them more than they are currently paying if they get into a protracted legal battle.