Apple Inc. says a new consumer study shows its iTunes online music store vaulted past Wal-Mart Stores Inc. in February to become the top overall music retailer in the U.S.

Apple said Thursday consumer surveys conducted by market research firm The NPD Group show iTunes' music sales surpassed those of the discount retailing giant in January and February.

ITunes has sold more than 4 billion tracks since its launch in 2003, thanks in part to the popularity of its line of iPod portable music players.

The NPD surveys count every 12 digital downloads as one CD. They exclude mobile music sales.

A call to NPD was not immediately returned.

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