iTunes Now Top U.S. Music Retailer

San Francisco Apple Inc. said on Thursday its iTunes online music store has surpassed Wal-Mart Stores to become the largest music retailer in the United States.

Apple's statement, citing industry data, came on the same day that iTunes faced a new challenge as News Corp.'s MySpace social-networking site said it had formed an online-music venture with three record labels.

The company said its announcement was based on consumer data collected in January and February by market-research firm NPD that counted 12 songs being equal to one CD.

In February, NPD said iTunes overtook Best Buy Co. and Target Corp. in 2007 to become the No. 2 U.S. music seller.

Apple said iTunes had 50 million customers who had bought more than 4 billion songs since the store opened five years ago.