Stocks eased on Monday, with airline shares hitting session lows in afternoon trading amid security worries.

The United States tightened airline security after a Nigerian man allegedly smuggled explosives aboard a transatlantic flight and attempted to blow up the plane. The NYSE Arca Airline index <.XAL> shed 2.8 percent.

The Dow Jones industrial average <.DJI> was down 12.02 points, or 0.11 percent, at 10,508.08. The Standard & Poor's 500 Index <.SPX> was down 2.89 points, or 0.26 percent, at 1,123.59. The Nasdaq Composite Index <.IXIC> was down 5.00 points, or 0.22 percent, at 2,280.69.