Q

Q (キュー, Kyū) is a software in the world of Hunter × Hunter.

Overview
By sending a nine-digit code to a phone company held by the Hunter Association, a Hunter can send and receive information via this special software. There are no logs and no call history, and regular wiretapping systems cannot detect this method of data transfer.

Dark Continent Expedition Arc
After Basho, Biscuit, Hanzo, Melody, Kurapika and Izunavi had sent their details to the six offers from Princes of the Kakin Empire, Kurapika reminds them that if their clients specified a non-disclosure agreement, they should be using Q as their method to share information between themselves.