The 1992 release Killing In The Name of by Rage Against The Machine was the best selling song in the UK last week. Why that came to be is an example of several ways in which the internet affects cultural life in 2009.

For many years there was a long-standing tradition in the UK of the “race” to be the number one single in the charts announced on the Sunday before Christmas Day. While rarely an example of musical excellence, the “battle” was something of a cultural icon which attracted media attention and even had bookmakers offering odds.

However, for the past four years, the race has been won by the relevant winner of X Factor, a reality show along the lines of American Idol, complete with Simon Cowell as judge. The show is always timed so that the winner releases a song in the week of the Christmas charts and taking the top slot has become an inevitability. That’s what three months of relentless prime time TV promotion will do.

Until this year.

In the past couple of years there have been unsuccessful campaigns to get another song to the number one slot. Most failed miserably and even the most likely (Jeff Buckley’s cover of Hallelujah, doing battle with the X Factor winner releasing the same song) only made it to a fairly distant number two.

This year a couple named Jon and Tracy Morter, who’d carried out similar attempts in the past, started a Facebook group to get Killing In The Name Of to the number one slot. And it went viral. And by viral I don’t mean that a few ad execs sent joking links to one another, but rather than it attracted just short of one million members.

The question was how many people would follow up on their pledge to buy the single. The answer was a stunning proportion: more than 500,000 did so, giving it an approximate 10% lead over X Factor winner Joe McElderry.

This isn’t just a case of social media allowing people to come together for a cause. It’s also an example of how digital music formats have changed the music charts. Since 2005, downloads have been included alongside CD sales in the UK charts. While several songs have reached the number one slot solely through downloads, this is only the second to do so without a subsequent physical release. It’s also the first time the inclusion of downloads has allowed a back catalog song to hit number one without a formal re-release.

While this isn’t exactly a case of Facebook changing the world, there has been some positive effects (beyond subjective views on musical tastes): the organizers of the campaign also asked people buying the song to donate to Shelter, a charity which helps homeless people. At the time of writing the appeal had raised £81,954 ($130,000), while it’s reported Rage Against The Machine will be donating their royalties from the week’s sales.