As global leaders and diplomats met Monday in Paris to say they would use "whatever means is necessary" to defeat the Islamic State group, key federal and regional officials held a summit of their own in midtown Manhattan to talk security.

Their message: Since Sept. 11, 2001, nothing has changed and everything has changed -- and we cannot let down our guard for even one second. What hasn't changed is our understanding that the New York City region remains America's top terror target. What's different is the nature of the threat. Today it's far more complex.

Yesterday's enemy, al-Qaida, has decentralized into a network of affiliates that mean to do us harm, explained Homeland Security Secretary Jeh Johnson.

And while the fighters known as ISIS represent an especially horrific threat to American values, other dangerous groups are lurking in the shadows as well -- including Hamas and Hezbollah -- said Gov. Andrew Cuomo. The possibility of homegrown terrorists working with any of these groups is all too real.

"It has been 13 years and you can get lulled into a false sense of security," the governor said earlier.

He has a point. Intruders have repeatedly breached heavy security to enter 1 World Trade Center recently. They've also scaled the Brooklyn Bridge twice -- even though it's under police surveillance 24/7.

And what about Mayor Bill de Blasio, the No. 1 leader of the No. 1 U.S. terror target, who apparently didn't bother to apply for federal security clearance until last week?

Cuomo and New Jersey Gov. Chris Christie said they have asked the heads of their state police and their local homeland security officials for a preparedness review. They expect answers in 10 days. The governors also said they will add personnel to meet any potential threats.

Those are welcome words.

But in the absence of a clear and present threat, balance and common sense and are also crucial.

After all these years, the region should know this drill by heart: We must stay alert, but we cannot be consumed by our fears.