“The fact of the matter is, this was a routine three-month approval that was under seal that was leaked,” Feinstein told MSNBC’s Andrea Mitchell, who followed up by asking if the source of the leak should be investigated.

“I think so,” Feinstein said. “I think we’ve become a culture of leaks now.”

The Justice Department has been ensnarled in controversy for its aggressive surveillance of reporters in an attempt to root out sources of national security leaks.

Feinstein on Thursday defended the NSA program, saying it had long been in existence and should have been well-known to members of Congress.

“We have sent out letters urging people to come in and look at [it],” she said. “We have debated this several times, more than a dozen times, in the Intelligence Committee. It has been the subject of Judiciary Committee hearings. It has been the subject of extensive debate and votes. There is nothing new in this program.”

“This is a routine ... court reauthorization of a program that’s been in existence for a very long time,” she added.

Feinstein said the program is a necessary defense against terrorism, and said the NSA is highly restricted in what it has access to.

“This program has very strong restrictions on it,” she said. “The only way it can be used is if there is strict scrutiny, reasonable … knowledge that this can connect to a terrorist attack, either underway, or under planning, or some conspiracy. Then the number can be looked at based on the person who is a suspected terrorist. Then you can see what numbers that individual is calling.”

Feinstein stressed that the program did not entail the surveillance of phone calls, but only the collection of phone numbers, and said that if the NSA wants a phone number, they have to go to court in order to seize it.