Sounds like the Department of Homeland Security (DHS) has taken a big step to keep us safer from terrorists in the sky. DHS Secretary Janet Napolitano announced today that 100 percent of passengers on domestic and international flights by U.S. airlines are now being matched against government watchlists through the Secure Flight program run by the Transportation Security Administration (TSA). Previously, individual airlines were responsible for matching passenger names against terrorist watchlists.

That’s all well and good. But here’s a remaining security gap:

Passengers on non-U.S. airlines—which make up nearly 10 percent of traffic at U.S. airports, according to the DHS news release—are not subject to watchlist matching. The TSA expects to close that gap by the end of 2010 by requiring direct international flights to the U.S. to use Secure Flight. Perhaps even more disturbing: Passengers under the age of 18 aren’t required to show identification to purchase an airline ticket or to pass through airport security. That was the case with three kids from Jacksonville, Florida, last week who went on a misadventure to Nashville. Thankfully they were just wayward youths—and not baby-face terrorists who could potentially pass through security without showing I.D.

Smart Traveler Mark Orwoll is International Editor of Travel + Leisure.