The Department of Homeland Security and FBI issued an intelligence bulletin to encourage law enforcement agencies to be watchful over the holidays.
"Terrorists may seek to exploit the likely significant psychological impact of an attack targeting mass gatherings in large metropolitan areas during the 2010 holiday season which has symbolic importance to many in the United States," the bulletin says, a copy of which was obtained by CNN. "We continue to assess, however, the timing of a terrorist attack depends more on terrorists' readiness to execute an attack rather than a desire to attack on a specific date."