Next » Matt Slocum - AP

A Philadelphia police officer, left, and a security guard walk past an entrance to the Wachovia Center before a preseason NHL hockey game between the Philadelphia Flyers and the Detroit Red Wings, on Tuesday, Sept. 22, 2009, in Philadelphia. U.S. counterterrorism officials have issued security bulletins on Monday, Sept. 21, about terrorist interest in attacking sports stadiums, entertainment complexes and hotels. (AP Photo/Matt Slocum)