The Homeland Security Department on Wednesday officially updated its terrorism alert system -- issuing a bulletin reminding Americans about the ongoing concerns regarding an attack on U.S. soil.

The bulletin was issued by agency Secretary Jeh Johnson, who reiterated that the government has no knowledge of a specific or credible terrorist threat against the United States but remains concerned about terrorist-inspired extremists.

This is the first change to the National Terrorism Advisory, as the system is officially known, since 2011 when the color-code system was replaced.

The system was put in place following the 9/11 attacks, when terrorists killed nearly 3,000 people in separate incidents in New York, Washington and Pennsylvania.

The bulletin issued Wednesday outlines much of what Johnson and other officials have said since the attacks in Paris last month and in San Bernardino, Calif., earlier this month. It will remain in effect until June 2016.

Johnson announced the change last week at a Defense One magazine event, saying, “We need a system that informs the public at large of what we are seeing.”

He also said the new system is “removing some of the mystery about the global terrorist threat, what we are doing about it and what we are asking the public to do.”

The bulletin is in addition to two other existing alert categories, elevated and imminent.

Johnson also said last week that the existing system has never been used because it has a “trigger that is a pretty high bar.”

In the California attack, reports indicate that one of the shooters, Tashfeen Malik, posted a statement about jihad on Facebook before entering the U.S. from Pakistan on a fiancée visa.

However, FBI Director James Comey has said investigators have no indication that Malik or her American-born husband, Syed Farook, were part of an organized terrorist cell or had direct contact with a foreign terror group.

Fox News’ Catherine Herridge and The Associated Press contributed to this report.