"No 100% guarantees" in homeland security, Napolitano says

Outgoing Homeland Security Secretary Janet Napolitano said homegrown radicals like the Boston Marathon bombers may be just as much of a threat to the U.S. as international jihadists.

"Boston happened. And I think that, you know, the kind of activity that Boston represents, one or two people making what, in fact, is a relatively low-tech type of improvised explosive device-- putting it along - or in a place where, you know, it's very difficult to protect an entire marathon route. That kind of attack is something that has been a key concern of mine, and I think of the head of the F.B.I.'s for-- for quite some time," Napolitano told CBS News.

When asked if Boston is a reminder that there's no way to prevent every terrorist act, Napolitano said, "what we can do is be always thinking about threats we could confront," but, she added, "there are no 100 percent guarantees in this business."

Napolitano added that the greatest transnational threat likely comes from al Qaeda in the Arabian Peninsula, a Yemen-based group which has repeatedly tried to target the U.S. with bombs aboard aircraft. And with the U.S. military poised to strike Syria, the Department of Homeland Security is also warning of possible retaliatory strikes including cyber attacks.

"We are always, as a department, thinking about-- you know, potential actions, threats, risks that we face. Some of them can be in the cyber world, which is a growing area of activity against our core critical infrastructure," Napolitano said.

While Napolitano is leaving the top Homeland Security job Friday to run the University of California, President Obama has yet to name a successor.

At a farewell ceremony Friday, Vice President Joe Biden lavished praise on Napolitano's four-plus years as secretary, calling her "a really, really bright lady," and suggested there's another high-profile Washington, D.C. job he would like to see her hold one day.

"I think Janet should be on the Supreme Court of the United States," he said. "That not only speaks to the other qualities I've mentioned about your character, but your intellectual capacity and your depth of knowledge."

Sensing his remarks would garner a bit of attention, given Biden's long, colorful history of shooting from the hip, he joked that his Supreme Court suggestion was pre-planned.

"My staff, when I said I was going to say this, said, 'Oh, don't make news.'"