The U.S. Postal Service pursued a project to build and secretly test a blockchain-based mobile phone voting system before the 2020 election, experimenting with a technology that the government’s own cybersecurity agency says can’t be trusted to securely handle ballots.

The system was never deployed in a live election and was abandoned in 2019, Postal Service spokesman David Partenheimer said. That was after cybersecurity researchers at the University of Colorado at Colorado Springs conducted a test of the system during a mock election and found numerous ways that it was vulnerable to hacking.