Ridge stated the action was based on a "substantial increase" in the frequency of intercepted transmissions indicating that extremist groups were anticipating attacks that would "rival or exceed" the the Sept. 11, 2001 attacks on the United States.
"The strategic indicators including al Qaeda's continued desire to carry out attacks against our homeland are perhaps greater now than at any point since Sept 11, 2001," said Ridge at a press conference.
Ridge also asked for the public to be patient with tighter security measures to be employed during the "coming days and weeks," but not to let the raised threat level interfere with holiday activities.
The terrorist threat level advisory system was put into effect following the Sept. 11, 2001 attacks on New York City and the Pentagon. Threat levels are:
Green - "Low" risk
Blue - "Guarded" or general risk
Yellow - "Elevated" or significant risK
Orange - "High" risk
Red - "Severe" risk
Also See: What to Do at Each Threat Level
