: Revoking unnecessary or high-risk approvals is a standard safety practice to prevent "drainer" attacks, where a compromised or malicious contract uses existing permissions to steal funds from a user's wallet.
This is the standard checksum formula used by legitimate software developers to verify that a credit card number is structured correctly before it is even sent to a payment gateway. It identifies typing errors but does not check if the account is active or has funds. Card-Not-Present (CNP) Fraud Prevention: Cronos Checker Cc