Which of the following is the MOST sensitive Personally Identifiable Information (PII) and should be shared cautiously and only with trusted resources?

An email address is PII, but it is generally less sensitive than a mother's maiden name as it does not typically serve as a singular critical security verification factor for high-value accounts.

A phone number is PII and can be used for multi-factor authentication, but it is often less uniquely tied to identity verification for account recovery than a mother's maiden name.

A mother's maiden name is highly sensitive PII because it is frequently used as a security question or a key factor in identity verification and account recovery processes for financial institutions and other secure services. Its compromise can directly lead to unauthorized account access or identity theft.

A last name is PII, but it is generally considered public information and has very low sensitivity for identity verification purposes on its own, unlike a mother's maiden name.