Track That Britney Left Out Of The Zone Is A Hit Online

'(I've Just Begun) Having My Fun' is a top-10 download on iTunes.

The latest Britney Spears song creating a buzz is actually an old song. No, not her upcoming cover of Bobby Brown’s ’80s hit “My Prerogative” — one of her own old songs.

“(I’ve Just Begun) Having My Fun” is a top-10 download on iTunes, thanks in part to fans speculating on Web sites and message boards that it’s a new song from the singer’s forthcoming greatest-hits album. The “new” tune, however, is actually from the In the Zone sessions.

The dance song — with an electro groove reminiscent of No Doubt’s “Hella Good” — describes a make-believe encounter with a boy at a party that made her feel a little wild but leaves her falling asleep in a chair. Lyrics to this song include “I’m just a crazy kind of girl/ I’ll tell it to the world/ I’ve just begun having my fun/ Inside me there’s something I’ve found/ I wanna shop around/ I’ve just begun/ Don’t wanna settle down.”

Spears worked on the song with producers Bloodshy & Avant, the same Swedish duo who worked with her on “Toxic” and her “My Prerogative” cover, which will be the first single from Greatest Hits: My Prerogative, due November 16 (see “Britney Makes Party-Crashing Her Prerogative In Next Video” ).

Just as the U.S. version of Spears’ “In the Zone” DVD included bonus tracks from the album of the same name’s recording session, so did the European DVD, where “(I’ve Just Begun) Having My Fun” was first released (the U.S. version includes “Don’t Hang Up” and “The Answer” as its bonus tracks).

The first time “(I’ve Just Begun) Having My Fun” saw Stateside release was through an exclusive deal last year with Wal-Mart and Sony Connect. That deal ended recently, leading iTunes to add the song on Tuesday to its available list of downloads, where it’s currently #7 on a list of songs that mostly includes more standard hits such as Ashlee Simpson’s “Pieces of Me” and Usher’s “Yeah!” The song is also available from Real’s Rhapsody service.