Seven of the nine ISIS jihadis who launched a series of coordinated terrorist attacks in Paris last November entered Europe by posing as refugees.

The attackers were part of a group of 14 who plotted their way into Western Europe by riding the wave of the migrant crisis last year, according to Hungarian security officials.

By using fake Syrian passports, many of the attackers, already on European terror watch-lists, were able to slip back into Europe undetected, along with thousands of other refugees.

One hundred and thirty people were killed in November when a group of gunmen and suicide bombers launched a wave of attacks across Paris, targeting the Bataclan concert hall, the Stade De France and several restaurants and bars. Three hundred sixty-eight people were also injured in the attacks, almost 100 of them seriously.

Some of the remaining terrorists in the group participated in the Brussels attacks earlier this year in three coordinated suicide bombings at Brussels Airport and at Maalbeek metro station killed 32 people.

Counterterrorism officials in Hungary believe ISIS set up a “logistics hub” in the country in the Summer of 2015 at the peak of the migrant crisis, with jihadis taking advantage of Europe’s porous borders to slip into Western Europe through Eastern Europe’s Balkan routes.

An investigation scrutinizing the phones used by some of the suspects found that one of the lead coordinators of the Paris attacks, Abdelhamid Abaaoud, sent a scout to report on the feasibility of using the Balkan routes as an entry point to Western Europe.

The group communicated with each another using social media applications such as Facebook and WhatsApp messaging, often creating and deleting their accounts within a day, as soon as they were able to obtain new instructions from Raqqa, Syria, where they were in contact with ISIS leadership, Hungary’s counterterrorism’s deputy chief General Zsolt Bodnar told The UK Times.

Aboud was killed in a raid by French counterterror police in the days following the Paris attacks.

Hungary voted Sunday to reject the E.U.’s migrant quota for the country. With turnout reported to be only 44 percent below the 50 percent threshold needed, the vote was set to be declared invalid.