Radiohead is releasing a haul of unheard archive music after the band was hacked and asked to pay a ransom.
Some 18 hours of material was stolen from frontman Thom Yorke's archive from around the time of 1997 album OK Computer, guitarist Jonny Greenwood said on Twitter.
The "only tangentially interesting" music was never intended for public consumption, he added.
In a statement on Twitter, Greenwood said: "We got hacked last week - someone stole Thom's minidisk archive from around the time of OK Computer, and reportedly demanded $150,000 on threat of releasing it."
Greenwood added: "So instead of complaining - much - or ignoring it, we're releasing all 18 hours on Bandcamp in aid of Extinction Rebellion.
"Just for the next 18 days. So for £18 you can find out if we should have paid that ransom."
He said: "Never intended for public consumption, (though some clips did reach the cassette in the OK Computer reissue) it's only tangentially interesting. And very, very long. Not a phone download."
Greenwood also tweeted links to Radiohead's page on music sharing site Bandcamp and to the website of climate campaign group Extinction Rebellion.
A note from lead musician Thom Yorke on the Bandcamp page says: "We've been hacked.
"My archived mini discs from 1995-1998(?). It's not very interesting, there's a lot of it."
He added: "As it's out there, it may as well be out there. Until we all get bored and move on."