As the Obama administration took tough action against Russia for interfering with the 2016 U.S. election this week, two experts in U.S. voting-machine security offered evidence at Europe’s largest annual hacker conference here they say proves that while the voting machines used in the November presidential election were not hacked, U.S. voting systems remain “shockingly” exposed to hackers. “We knew on November 8 that hacking was possible,” J. Alex Halderman, a University of Michigan computer science professor who specializes in testing voting-machine security, said Wednesday in front of a crowd of more than 1,000 attendees of the 33rd annual Chaos Communication Congress. Prior to Election Day, as Donald Trump repeatedly claimed that the election would be “rigged” against him, email servers belonging to the Democratic National Committee and Clinton campaign manager John Podesta, as well as voter registration systems in Illinois and Arizona, were hacked. And after the election, which resulted in Hillary Clinton winning the popular vote by a substantial margin but Trump winning more votes in the overriding Electoral College, many people, including Green Party candidate Jill Stein, called into question whether votes had been tallied without interference. Trump also alleged on Twitter that if it wasn’t for “the millions of people who voted illegally,” he would have won the popular vote. “Shockingly—at least shockingly to me and many other people, even under these circumstances—approximately zero U.S. states were going to look at enough paper ballots to know whether the computers had been hacked,” Halderman said. “This is a major gap in our system.”