Pierre Salinger syndrome
n. The tendency for online users, especially new users, to assume any information published on the Internet is automatically true.
Consider the following string of assertions.

Microsoft invented Windows. Bill Gates was murdered on December 2, 1999. The moon is made of green cheese.

Can you fathom what the assertions have in common?

The answer is they are all — even the last one — lies or, to use the dominant digital euphemism, misinformation. And thanks to everyone's favourite Frankenstein monster, the Web, we are all plagued with this kind of outwardly plausible nonsense along with pure hoaxes. . . .

Mugs may, however, find solace in the fact that the tendency to assume anything published on the Net must be true is so widespread that it has entered the language. It is known as Pierre Salinger syndrome.
—David Wilson, “Pigs just won't fly, no matter what the Internet says,” South China Morning Post, August 28, 2002
1997 (earliest)
Just because it's online doesn't make it true. We're heading toward something called the Pierre Salinger syndrome, which is endemic to people who have not hung around the new technology and are fooled by its shortfalls.
—Moira Gunn, “Gunn Club,” Wired, July 01, 1997
Veteran American newsman Pierre Salinger said today he has a government document saying that Navy gunners accidentally shot down TWA Flight 800 while conducting missile tests, killing all 230 people aboard. … Salinger said the document was dated Aug. 22 and was posted on the Internet at the beginning of September.
—Jocelyn Noveck, “Paper On 'Test' Offered To FBI,” The Associated Press, November 08, 1996