Taylor Swift has hinted she's re-recording one of her old songs with Keith Urban.

The pop star dropped a cryptic video message on Friday and challenged fans to decode anagram clues that popped out of a gold vault.

"The vault door is about to be as unhinged as you'll think I am after you watch this video," she wrote on Twitter, alongside a video that featured scrambled words flying out of a vault door. "Level: Expert. Happy decoding!"

Fans were quick to figure out the clues, scrambling the song titles We Were Happy, Don’t You, Mr. Perfectly Fine, Bye Bye Baby, and That’s When, while Keith's name also popped up, with fans suggesting he will be appearing on one of the new songs Taylor is releasing from her Fearless album sessions.

It's not clear on which one Urban will feature, but superfans noted the song playing in the background of the vault video was Don’t You.

The full album will be released on 9 April.

Swift is re-recording her old songs to thwart the new owners of her former record company - and her back catalogue - from making any money from her hits.