A report from the head of European police agency Europol claims that around 5,000 European Union citizens have so far joined the ISIS. All the European governments are well aware of this fact and are working hard to check the trend of their young men to leave the country in a bid to fight for the ISIS. But the greatest matter of concern to the security officials of the countries is that these young men pose a threat to their country of origin if they return there. The latest example is the terrorist attacks in Paris in the last week. So, it is really a matter to be worried about.