Frequency
From Tardis Wiki, the free Doctor Who reference
"ChatGuest1" sent the readers of Defending the Earth! to the page about Vitex on the Cybus Industries website to look for the number for that day's "special frequency or wavelength"; the number turned out to be hidden in plain sight on a Cybus FM banner on the Cybus Fitness website, which had been advertised on the Cybus website. (GAME: Cybus Spy)
