To prevent terrorists and other criminals from exploiting the nation's immigration system.

"What we're trying to do," he added, "is prevent terrorists from depriving us of the free society that we've enjoyed for two centuries."

The emphasis, the British pilots' union said, "must be on preventing potential terrorists from boarding aircraft."

What is being done internationally to prevent terrorists acquiring nuclear weapons?

Powers must escape the hospital, find out who framed him, piece together his memory, and prevent terrorists from blowing up a peace conference.

"It is vital to prevent terrorists from entering Japan and to ensure that their activities are contained."

He said the fence would prevent terrorists from getting to his family.

That means we must prevent terrorists from entering this country before they act.

The new agency's primary mission was to prevent terrorists and their weapons from entering the United States.

They were removed to prevent would-be terrorists from dropping package bombs in them.