Millions around the world are preparing to commemorate the Sept. 11 terrorist attacks that claimed the lives of nearly 3,000 Americans.
On Tuesday, Defense Secretary Leon Panetta will host an event at the Pentagon, and Vice President Joe Biden will speak in Shanksville, Pa.
The Associated Press reports that Americans feel safer today from potential terrorist attacks than they did a few years ago, a sentiment affirmed by military experts.
According to a new law enforcement bulletin, the successful targeting of al Qaeda leaders has led to a decline in threats of a 9/11-style attack from the global terrorist group.
"Twenty-three of the top 30 al Qaeda commanders are off the field -- either dead or captured in the last two, three to four years. So this has been a pretty tough series of months and years for al Qaeda," Michael Breen, vice president of the Truman National Security Project, said.
But 11 years after the tragedy that changed the country, authorities warn that America is still vulnerable.
"There is probably some worry on the part of intelligence officials that bad guys have the ability to hit us, are likely to hit us on a day like 9/11," former NYPD Intelligence Analyst Samuel Rascoff said.
The administrations of both George W. Bush and Barack Obama have made dismantling al Qaeda a top priority, and they've been largely successful.
Just this week, an air strike killed the terrorist networks number two leader in Yemen.
"The al Qaeda organization that hit us on 9/11 more or less is on the run to the point where it might not even exist years from now," Rascoff said.
But military and national security experts warn that in some areas the United States is more vulnerable than ever. Topping the list is cyber security.
"A lot of people talk about a digital Pearl Harbor where you'd go in and you'd have a cascading series of systems in failure, and you'd take down the electrical grid and everything starts to cascade from that, and essentially the whole country goes black," James Carafano, a security analyst with the Heritage Foundation, said.
Former CIA Director James Woolsey told CBN News that while al Qaeda may be weaker, the Lebanese-based Iranian proxy, Hezbollah, is gaining strength and is capable of launching a cyber-attack.
"Terrorists groups are a major, major concern," he warned. "Some of the things they might get involved in -- as far as hacking into our electric grid and the rest -- could be devastating. And Hezbollah has historically had the money to learn a lot and do a lot, and I would first and foremost be concerned about them."
Mexican media reported the arrests of three suspected Hezbollah members last weekend, one who is a U.S. national.
Meanwhile, at a conference Monday, Homeland Security Secretary Janet Napolitano warned that cyber warfare is one of the most rapidly evolving threats our country faces.
She said for the nation to successfully prevent a future cyber attack, the federal government and the private sector must improve the way they share information.