Homeland Security Lowers Trasit Alert

Does Homeland Security need to announce what level of security they are recommending? Isn't that giving information to potential terrorists? It doesn't make sense. They can monitor that on their own and increase or decrease security as needed. If there is a specific threat, then alert people, but it goes up and down and the whole workd knows it.

http://ap.tbo.com/ap/breaking/MGBHRTS3BCE.html