(AP) - Intruders got past security fencing or gates at least four times at Newark Liberty International Airport over the past decade.

On Christmas Day 2013, a man scaled a security fence and walked across two runways before trying to enter a terminal. Other incidents were in 2011, 2006 and 2005. That tally was based on news stories, though officials provided additional details for several.

An Associated Press investigation found there have been at least 268 perimeter security breaches at 31 major U.S. airports between January 2004 and January 2015. Intoxicated drivers crashed through barriers. Mentally ill intruders tried to hop flights. No incident was terrorism-related.

Airports say breaches are relatively rare. Security measures include fences, cameras and patrols, but not all fencing is routinely patrolled or covered by video surveillance.