RealNetworks, which sells songs over the Web, said Apple Computer has altered the software for some of its market-leading iPod digital music players so that songs purchased from...

RealNetworks, which sells songs over the Web, said Apple Computer has altered the software for some of its market-leading iPod digital music players so that songs purchased from RealNetworks won’t play.

The changes affect the new iPod Photo, RealNetworks spokesman Matt Graves said in an interview yesterday.

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Seattle-based RealNetworks in August released its Harmony program to enable its music to be directly downloaded to iPod devices, bypassing Apple’s copy-protection software.

RealNetworks introduced Harmony, which allows music to be downloaded to a range of devices, to differentiate its music store from offerings by Microsoft, Apple, Wal-Mart and others. Apple’s iTunes is the most popular store, and Apple is protecting that lead by designing its software so other stores can’t load their music directly onto the iPod.

“It is highly likely that Real’s Harmony technology will cease to work with current and future iPods” because of software updates, Apple spokeswoman Natalie Kerris said in a statement. She declined to comment further.

Apple has updated the software for all of its iPod models in the past two months, according to its Web site. RealNetworks, which is trying to fix the problem, doesn’t know how many iPod models can’t play its music, Graves said.

The software changes are the latest move in a battle between RealNetworks and Apple that began in April after Apple Chief Executive Steve Jobs refused an e-mailed request from RealNetworks Chief Executive Rob Glaser to open up the iPod to RealNetworks’ music.

RealNetworks responded by designing Harmony without Apple’s assistance. The company released a test version in July to complaints from Apple that RealNetworks had “adopted the tactics and ethics of a hacker.” Apple said then that Harmony might not work on future iPod updates.

Apple’s iTune stores are the No. 1 destination for buying music over the Internet, accounting for almost 70 percent of music sold legally between December 2003 and July 2004, according to researcher NPD Group.

RealNetworks’ music store had 6 percent of the market, putting it in a tie for third place with Wal-Mart and MusicMatch. Roxio’s Napster site was ranked No. 2 with 11 percent, NPD Group said.