Apple has announced that the iTunes Store has surpassed Wal-Mart to become the number one music retailer in the US, based on the latest data from the NPD Group.

Last month it was similarly revealed that Apple had beaten Best Buy to take the number two music retailer slot in the the US for December.

Apple says with over 50 million customers, iTunes has sold over four billion songs and features the world's largest music catalog of over six million songs.

"We launched iTunes less than five years ago, and it has now become the number one music retailer in the world", said Eddy Cue, Apple's vice president of iTunes.

"We are thrilled, and would like to thank all of our customers for helping us reach this incredible milestone."

The claim has raised some eyebrows in the tech world, not only with how the conclusion was reached - that 12 individual downloads equals an album's worth - but because the claim relates to figures from January 2008, a period influenced by Christmas gift cards and which saw a lull in big album releases.