A preview of Adele's James Bond theme song has been leaked online.

The track ' named Skyfall, after the movie ' wasn't due for release until Friday, but appeared on free music streaming site SoundCloud today.

The song has now been removed, but versions of it have been appearing on YouTube.

Adele confirmed her involvement with the song yesterday, when she posted a picture of the front page of the score on her Twitter page.

Response to the leaked track has been overwhelmingly positive, with fans comparing Adele's version to Shirley Bassey numbers like Diamonds Are Forever, which featured in the 1971 Bond film.

Adele said she was hesitant to record the track at first.

"There''s a lot of instant spotlight and pressure when it comes to a Bond song. But I fell in love with the script and Paul had some great ideas for the track and it ended up being a bit of a no-brainer to do it in the end,' she said.

"It was also a lot of fun writing to a brief, something I''ve never done, which made it exciting. When we recorded the strings it was one of the proudest moments of my life. I''ll be backcombing my hair when I''m 60, telling people I was a Bond girl back in the day, I''m sure."

Skyfall, starring Daniel Craig, hits theaters this month.