Answer: C
WPS attack
Explanation:
It is most likely a WiFi protected setup (WPS) attack. Reaver is a automated program that can brutally force attack an access point WiFi to discover its PIN. Once the PIN is discovered, it can be used to uncover the paraphrase or secret code used by the access point (AP).
Also, the attack typically does not show any sign to an average user as it is mostly undetected.