Some 18 hours of material was stolen by hackers from frontman Thom Yorke's archive, who then requested a ransom of around 150,000 U.S. dollars. The band is charging £18 ($23) for the download, with proceeds going to Extinction Rebellion.
Thom Yorke gets hacked and 18 minidisc files of OK Computer sessions are stolen (lasting 15 hours).
Fans can buy the music for $A25 for the next 18 days.
"It's not v interesting", he added.
In 2017, Radiohead released a deluxe version of their groundbreaking album that included three previously unreleased songs - "I Promise", "Lift" and "Man of War" - along with a cassette tape of select demos. "There's a lot of it... as it's out there it may as well be out there until we all get bored and move on".
In response, Radiohead have went and ahead re-leaked the entire 18 hours via Bandcamp.
"OK Computer" met with universal praise upon its release and helped forge the legend of a band that would become one of the most acclaimed of the next two decades.
In December 2018, Radiohead joined the Rock & Roll Hall of Fame, alongside Janet Jackson, the Cure, Def Leppard, Stevie Nicks, Roxy Music and the Zombies.
Radiohead are turning a ransom attempt into a win for the environment.
Activists from Extinction Rebellion - a fast-growing movement founded past year by British academics - want world governments to slash greenhouse gas emissions to zero by 2025.
Police arrested more than 1,130 people during the London protests, at which more than 10,000 police officers were deployed.