If Facebook notices unusual behavior (e.g., multiple failed login attempts, logins from a known hacker IP address), it will lock the account and demand a six digit code to prove ownership before allowing access.
The Facebook six-digit code provides a meaningful security improvement over password-only authentication but is not invulnerable. Its greatest weakness lies in the SMS delivery channel and susceptibility to real-time phishing. As account takeover attacks evolve, Facebook must shift toward phishing-resistant factors (passkeys, WebAuthn) while maintaining a simple fallback mechanism for users who lose access to their authenticator. For users, understanding that except the Facebook login screen is the single most effective defense.
