U.S. Homeland Security Secretary Janet Napolitano announced on Thursday that the current color-coded terror alert system will be replaced with a new two- tiered system.

"Today I announce the end of the old system of color-coded alerts. In its place, we will implement a new system that is built on a clear and simple premise," Napolitano said during a speech at George Washington University in Washington, D.C..

"When a threat develops that could impact you -- the public -- we will tell you. We will provide whatever information we can so you know how to protect yourselves, your families, and your communities," she said.

The current terror alert system, which uses five colors to represent different levels of terrorist threat, was created in March 2002 by then president George W. Bush, but was widely criticized as being confusing and too vague.

Under the new system, there will be two levels of threat -- " imminent threat" and "elevated threat," Napolitano said.

When there is information about a specific, credible threat, the department will issue a formal alert. Depending on the nature of the threat, the alert may be limited to a particular audience, like law enforcement, or a segment of the private sector, like shopping malls or hotels, said the secretary.

The alert may also be issued more broadly to the public, distributed -- through a statement from the department -- by the news media and social media channels.

The department on Thursday was beginning a 90-day implementation period in which federal, state and local government, law enforcement entities, private sectors, airports, and other transport hubs will officially transition to the new system.

"This means that the days are numbered for the automated recordings at airports, and announcements about a color code level that were, too often, accompanied by little practical information, " said Napolitano.

Under the current color-coded system, green, at the bottom, signals a low danger of attack; blue signals a general risk; yellow, a significant risk; orange, a high risk, and red, at the top, warns of a severe threat. The government has been keeping the national terror alert level at yellow since 2006.