How can a knowledge base learn from the Internet, when you shouldn't trust everything you read on the Internet? CORONA is a system for building a knowledge base from a combination of reliable and unreliable sources, including crowd-sourced contributions, expert knowledge, games with a purpose (GWAP), automatic machine reading, and even knowledge that is imperfectly derived from other knowledge in the system. It confirms knowledge as reliable as more sources confirm it or unreliable when sources disagree, and then by running the system in reverse it can discover which knowledge sources are the most trustworthy.