The story
Proposed as a transhumanist thought experiment in 2010 by user Roko on the LessWrong Internet discussion forum. According to LessWrong, discussion of Roko's basilisk was banned from the forum for several years as part of a general policy against spreading potential information hazards. This in fact drew further attention to the topic, and other websites began sharing information about it.
Etymology from Wiktionary, CC BY-SA 4.0.