______ is a social engineering trick where an intruder may follow an authorized user through a door that the authorized user opens with an access device.

• A. Shoulder surfing
• B. Shadowing
• C. Trailing
• D. Piggybacking

Answer: (D)

Piggybacking is a social engineering technique where an intruder follows an authorized user through a secure door after the user has opened it with an access device. It relies on the natural courtesy or distraction of the authorized person who doesn’t challenge or deny entry, allowing the intruder to slip in without presenting their own credentials. This specific scenario is distinct from shoulder surfing, which involves watching someone enter a password or PIN to capture credentials, not gaining physical access. While shadowing or trailing describe following someone, piggybacking is the term that most precisely captures the act of entering a secured space by riding along with someone who has legitimate access.