What method limits the number of attempts to crack a user account password by trial and error?

The method that effectively limits the number of attempts to crack a user account password by trial and error is locking out the account after a specified number of failed login attempts. This security measure is commonly implemented in systems to mitigate the risk of unauthorized access through brute-force attacks, where an attacker systematically attempts various combinations of passwords until the correct one is found.

When an account is locked out due to repeated failed login attempts, the user cannot attempt to log in again until the lockout period expires or until an administrator manually unlocks the account. This significantly reduces the time and opportunity for an attacker to guess the password, making it a robust defense mechanism.

Other methods, like password complexity and two-factor authentication, enhance security but address different aspects of account protection. Password complexity ensures that users create strong passwords, while two-factor authentication adds an additional layer of verification beyond just the password. Account expiration involves limiting the timeframe for which an account can be used but does not specifically restrict password guessing attempts.