: Change your passwords immediately if you have reused them across different sites. Use a Password Manager to ensure every account has a unique, complex password.
If you are researching this for security purposes or believe your account may be involved:
: Use authoritative tools like Have I Been Pwned to check if your specific email was part of a known breach.
: These lists are rarely from a single "Yahoo breach." Instead, they are typically aggregations (collections) of data stolen from various smaller websites where users happened to use a Yahoo email address to register.