Napolitano said that Snowden caused the U.S. harm when he leaked documents about the country's surveillance operations.
"I think Snowden has exacted quite a bit of damage and did it in a way that violated the law," she said. "He has, by individual fiat, leaked very extensive information."
She said that while the U.S. does need to strike a balance between privacy and security, Snowden took matters into his own hands.
"There is a balance, the right balance, to be struck here," she said. "Mr. Snowden just decided to go off on his own, and he did exact quite a bit of damage, in my judgment."
Watch the video via NBC: