Under pressure to prevent people from sneaking onto runways and planes at major U.S. airports, authorities are cracking down -- not on the intruders who slip through perimeter gates or jump over fences, but on the release of information about the breaches. A year after an Associated Press investigation first revealed persistent problems with airports' outer defenses, breaches remain as frequent as ever -- about once every 10 days -- despite some investments to fortify the nation's airfields.