Al Franken edged back into the spotlight Tuesday, speaking at a cybersecurity conference in Lisbon, Portugal, four months after resigning from the U.S. Senate amid sexual misconduct allegations.

The Minnesota Democrat criticized tech giants for carelessness with users' data and said that more federal regulations might be necessary to constrain their conduct.

"Facebook doesn't have to care about the privacy and security of their users' online information because there's no mass exodus when it violates those rules," he said at the Privacy Xchange Forum hosted by security company CyberScout.

"They have no real competitors … and that means users have no defense."

He was describing the response of Facebook founder Mark Zuckerberg to reports that data firm Cambridge Analytica had gained access to 87 million Facebook users' private information.

"Why didn't Facebook do anything? Why did it take so long?" Franken asked. "I think it's because they knew they could get away with it."

Franken made no reference to the end of his Senate career. He spoke in serious tones and suggested that Congress must act to protect Americans' privacy — and democracy.

"If we can't have a political discourse where we agree on basic, objective facts … then our democratic government will continue to be polarized and paralyzed," he said.

Franken left the Senate after being accused by several women of inappropriate touching as the #MeToo movement was taking root. "I may be resigning my seat, but I am not giving up my voice," he said Dec. 7 on the Senate floor.

He denied some allegations and apologized for his actions, but Senate Democrats demanded that he step down. Democrat Tina Smith was named by Gov. Mark Dayton to complete Franken's term.

Franken's last public appearance was on Dec. 28 in Minneapolis. In March, he re-emerged with a Facebook post accusing Attorney General Jeff Sessions of a lack of candor during exchanges between the two men at Sessions' confirmation hearing.

J. Scott Johnson, a political science professor at the College of St. Benedict and St. John's University, expects Franken to gauge public response to his speech Tuesday as he decides whether to speak out more often.

"Cybersecurity in Lisbon is a long way from a comeback," Johnson said, "but it's probably an important first step."

Fred Slocum, an associate professor of political science at Minnesota State University, Mankato, said "there are a number of ways in which he can still remain active in public life."

He could be an advocate for a nonprofit group, serve on corporate boards, become a scholar or host a political TV show, Slocum said.

During a question-and-answer session in Lisbon, Franken, 66, displayed a bit of his trademark humor when he was asked if the U.S. election system is secure.

"I think it's completely secure and we have nothing to worry about," he said with deadpan delivery. He waited a beat and smiled before saying, "I think it isn't secure and I worry about that a lot."

He added a warning about Russia's meddling: "They'll be back. They never left."

A Franken aide said that he has no additional public appearances scheduled. Sen. Amy Klobuchar, D-Minn., said last month that Franken has "had two acts and he's still going to have a third."

Judy Keen • 612-673-4234