Paris attacker exploited Turkey's porous border

TURKEY -- A major difficulty in the fight against ISIS is that they often slip their fighters through borders and use fake passports which is how at least one of the Paris attackers entered Europe through Syria.

Paris attacker apparently traveled from Syria with refugees

The flood of refugees from Syria makes controlling who gets into a country more difficult reports CBS News' Holly Williams. At least six of the terrorists in the Paris attacks are thought to have spent time in Syria, and at least one of them was known to the French authorities as an extremist; but that extremist still managed to enter France by posing as Syrian refugee.

Secretary of State John Kerry announced new measures to secure Turkey's border, but there is no guarantee that the effort will be effective.

The border is 500 miles long, and Turkey has already increased security. A senior Turkish official told Williams on Tuesday that it is impossible to cut off the flow of extremists through the border.

The Turkish official also pointed out that there is a problem with intelligence sharing, and said that Turkey warned France about one of the terrorists, twice. Concerns were that the terrorist would travel to Europe from Syria.

He said French officials only followed up with Turkey after the attacks in Paris.