"Just think about how dangerous that is, how third world that is of a practice," Trump told Fox News' Maria Bartiromo. "Just think about it."
"It's really sad that we're in an environment where tax returns are leaked by whoever it may be," he said. "When personal information is put out by people for political agendas. As a civilian, it's actually scary to me."
His brother Donald Trump Jr. on Tuesday night went on a tweetstorm thanking MSNBC host Rachel Maddow for revealing part of their father's 2005 tax returns on air.
"Watching the media aka #fakenews implode on tv now because they got what they wanted is simply awesome," he tweeted, using the hashtag #ThankYouMaddow.
President Donald Trump refused to release his tax returns throughout the 2016 campaign and after his election and claimed he was under audit.
The White House nevertheless confirmed the numbers in the tax return moments before Maddow's show aired on Tuesday night.