Estonia is the only country in the world that relies on Internet voting in a significant way for legally-binding national elections — up to 30% of all voters cast their ballots online. This makes the security of Estonia's Internet voting system of interest to technologists and citizens the world over. Over the past year, I helped lead the first rigorous, independent security evaluation of the system, based on election observation, code review, and laboratory testing. The findings are alarming: there are staggering gaps in Estonia's procedural and operational security, and the architecture of the system leaves it open to cyberattacks from foreign powers. Our investigation confirmed the viability of these attacks in the lab, but the Estonian government has chosen to downplay them. We urgently recommend that Estonia discontinue use of the system before the country suffers a major attack.