The Publius Enigma is an Internet phenomenon (and potentially an unsolved problem) that began with cryptic messages posted by a user identifying only as "Publius" to the unmoderated Usenet newsgroup alt.music.pink-floyd through the Penet remailer, a now defunct anonymous information exchange service. The messenger proposed a riddle in connection with the 1994 Pink Floyd album The Division Bell, promising that the answer would lead to a reward. It remains unclear if the enigma involves a genuinely solvable puzzle as part of an early Internet-based contest or was a convoluted hoax engineered in part by the band's management. Regardless, the mystery continues to attract a small but loyal cult following.
More information and links on the Wikipedia page