"We have to toughen our surveillance, our interception of communication," the former secretary of state and Democratic presidential contender said Tuesday in an interview with CNN's Wolf Blitzer.
Clinton continued: "We have to also toughen, as you say, 'soft targets,' with greater police presence -- there is no getting around that."
Her comments come in the wake of the latest strike on European soil for which ISIS has claimed responsibility. At least 30 people were killed in the attacks in Belgium's capital.
Clinton said terrorists are "getting more sophisticated" in their construction of explosives to escape detection.
"We have to continually be learning and getting ahead of these thugs and criminals in order to prevent them doing what they did in Brussels," she said.
In the interview, Clinton called for increased information-sharing between the United States and European countries.
She broke with Donald Trump's Monday criticism of the U.S. role in NATO. The Republican front-runner had declared that the United States is spending too much money in the trans-Atlantic organization.
"I'm a very strong supporter of NATO. It's the best international defense alliance I think ever," Clinton said. "We have to keep adjusting and changing its mission to meet the new threats that we as members of NATO face. I think it would be a grave error to walk away from Europe, to walk away from NATO."
She added: "I think NATO has a role to play. I would certainly as president and commander-in-chief be looking to define that role, to make sure that the capacity, the tools and assets that NATO has are at the disposal of member nations like Belgium during this terrible event that they are experiencing, and then let's see what more we can do."
Clinton wouldn't, though, respond to Trump's overall insults.
But she invoked a sore spot for Trump -- hands -- in saying: "We need steady, strong, smart minds and hands in the White House, in the Situation Room, to deal with the problems we face around the world."
The former secretary of state dismissed criticism from Republicans -- including Trump -- that she won't use the phrase "radical Islamic terrorism," saying she prefers "radical jihadist terrorism" and that the wording is "a long debate that people like him try to stir up."
"I don't think you get that kind of cooperation that I'm looking for -- deep, intense, long-lasting cooperation -- by playing these semantic games," Clinton said.