This is allegedly a leaked, unaltered recording of Britney Spears singing "Alien"—from her 2013 album Britney Jean—without the benefit of Auto-Tune, pitch correction, or any of the other studio tricks that featured heavily on the album. It sounds a teeny bit different from the finished track.
Although Brit-Brit's most fervent fans on YouTube claim this version has been altered to make her sound intentionally off-key, producer William Orbit all but confirmed it was the real deal while defending the singer from her haters:
I'd like to affirm that ANY singer when first at the mic at the start of a long session can make a multitude of vocalisations in order to get warmed up.
Warming up is essential if you're a pro, as it is with a runner doing stretches, and it takes a while to do properly. I've heard all manner of sounds emitted during warmups. The point is that it is not supposed to be shared with millions of listeners.
A generous singer will put something down the mic to help the engineer get their systems warmed up and at the right level, maybe whilst having a cup of herb tea and checking through lyrics before the session really kicks off. It's not expected to be a 'take'.
He's got a point: No matter how bad it sounds (pretty bad), it's not as if Britney intended this take, if it's real, for release. By all means, feel cheated by the final product—it was no "Toxic," after all—but if you're shocked to find out that a popular singer uses Auto-Tune, I've got a T-Pain Memorial Bridge* to sell you.
*T-Pain is actually still alive.
[H/T The Verge]