Virtually every major new media technology, from the printing press to lithographs to radio and TV, have been adopted early by cranks and conspiracy theorists.
So it went with the nascent internet which was immediately embraced by cranks. A 1999 book called “Conspiracy Theories: Secrecy and Power in American Culture” describes the early 90’s USENET as a fertile garden of posts about government plots, UFO’s, JFK, and “on topics such as who runs the Federal Reserve, Lyndon LaRouche’s [conspiracy] theories, and the credibility of well-known conspiracy theorists.”
When the September 11th attacks hit, then, the internet was perfectly poised to become a virtual ground zero of accusations that the attacks were “an inside job.” For years, conspiracy theorists and skeptics battled it out over the tiniest details about the attacks, with a variety of plots put forth (The government did it with bombs! The government let it happen to invade Iraq! The Pentagon was hit by a missile fired by…someone! Flight 93 was shot down! The planes never existed!”) and beaten back with evidence.