Super Furry Animals' forthcoming album is being traded online - three months before its official release.
Gruff Rhys' voice was under wraps until 14 July
July proved too long to wait for some fans, who are listening to a leaked pirate copy of Phantom Power now doing the rounds on file-sharing networks.
They are able to download mp3 files of the entire recording - the latest example of online music piracy.
But the Welsh band, which has previously given a thumbs-up to file-sharing, has promised CD-only bonus extras on the eventual release.
The Welsh experimentalists were expected to preview album tracks at June's Pesda Roc festival before releasing their sixth recording on 14 July.
But a copy of Phantom Power fell into the hands of a pirate group called Escape, which starting spreading it around the internet over the Easter weekend.
Record labels are struggling to stop copying and swapping
The band refused to comment, but a spokesman said: "I suppose it was going to be inevitable, but this is earlier than we expected."
The quintet recorded the album at its own Cardiff studio and the Rockfield and Monnow Valley studios in Monmouthshire. It was mixed in January.
It is a collection of trademark psychedelic rock tinged with techno touches, on which instrumentalist also Huw Bunford sings for the first time.
But it is not clear how the recording became available.
"It could be anybody, there's no use pointing the finger," said Gary Farrow of record label Sony Music.
Furries fans can expect special features on the CD
"We're not particularly happy about it and it's not the final copy.
"Changes have been made and there will be loads of bonus things on the CD that will not be available on the net, that's for sure.
"On the up side, it just goes to show how much interest there is in the band at this stage - it has been received as their greatest album yet."
Music copyright expert and Welsh Music Awards organiser Rhys Evans said: "I really don't know where these leaks come from.
"The band has embraced new technologies with their DVDs, but online distribution should be the Furries' choice.
People think that, because artists make money out of their music, they can take it for free
"For someone to take that choice away from them is bad and dangerous.
"File-sharing technology is great because it lets people share music, but it should be done responsibly."
Online music piracy is a huge annoyance for record companies, despite industry efforts to shut down software which lets computer users swap songs.
Radiohead were angered in April when a rough edit of forthcoming album Hail To The Thief was leaked to the web ahead of its 9 June release.
Some artists, like Madonna, are now posting decoy tracks online, trying to flood out the pirates with files that play nothing more than warning messages.
Internet copying is to blame for a 4% slump in UK sales, according to the British Phonographic Industry.