The novel War Of The Worlds was published in 1897 by H.G. Welles. Orson Welles made a radio adaptation of the book in 1938. When it aired on October 30th, 1938, 12 million people tuned in, and what they heard startled them. Instead of realizing it was adapted from the book itself, people thought they were ACTUALLY being invaded. It sounded incredibly realistic, and was formatted as a news broadcast, informing the public of objects falling from the sky in New Jersey, explosions on Mars, and widespread invasions all over the Earth. Public panic ensued and the broadcast was cut short.
This occurred because of the widespread fear of World War II, and people thought this faske news broadcast on CBS was real.
So, the major difference is that when people read the book, they knew it was fake, but when people heard the radio adaptation, they thought it was real!