http://www.fbi.gov/pressrel/pressrel01/skyfall.htm

Certain information, while not specific as to target, gives the government reason to believe that there may be additional terrorist attacks within the United States and against U.S. interests overseas over the next several days. The FBI has again alerted all local law enforcement to be on the highest alert and we call on all people to immediately notify the FBI and local law enforcement of any unusual or suspicious activity.