APPLE’S iTunes online music store has surpassed Wal-Mart Stores to become the largest music retailer in the US, the company said overnight.

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

News Corp is the parent company of the publisher of

Apple 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 and Target in 2007 to become the second largest US music seller.

Apple, which makes iPod media players, Macintosh computers and the iPhone, said iTunes had 50 million customers who had bought more than 4 billion songs since the store opened five years ago.

Shares in Apple rose 2.8 per cent to close at $US151.61 ($164) amid a 1.9 per cent gain in the broader Nasdaq market.

The stock is about 25 per cent below its all-time high hit in December, but has risen 25 per cent in the last month amid signs consumer worries over the economy have not dampened Apple’s sales.