Europol warns return of 5,000 potential terrorists may pose biggest threat to EU since 9/11

While warning Europe about the possible return of nearly 5,000 potential terrorists to the continent from the Middle East, the Europol has termed the threat "the biggest" since New York's Twin Towers were destroyed.

Rob Wainwright, the director of Europol, cautioned MPs that about 3,000 to 5,000 European Union nationals, who have travelled overseas, could pose significant threat to their home countries and launch "Paris-style" attacks if they returned, reported Sky News.

Terming the threat the "most serious" that Europe has faced since 9/11; Wainwright added that there have been significant developments in both the scale and variation of that threat. One of the most important evolutions in the current terrorist threat is the way the internet is used, much more "aggressively" and "imaginatively," he said.

Wainwright added that social media was no more just a recruitment tool but a propaganda tool and urged internet companies to do more to tackle terrorist activity online.