An attacker exploited a concurrency bug and created 2.25 billion XLM. In a statement to Messari, Stellar said that they had mentioned the bug twice in their release notes where they made it clear that the bug was exploited
As per Messari Research, Stellar suffered an inflation bug in 2017 which created over 2 billion XLM. Stellar has since patched this with an equivalent token burn. While researching the supply details of the top 50 crypto assets, they discovered: