CNET News.com reports that Apple has quietly updated its iPod firmware so that songs purchased from the RealNetworks music store will not play on iPod photo models. “The move could render tunes purchased by many iPod owners unplayable on their music players. For the last four months, RealNetworks has marketed its music store as the only Apple rival compatible with the iPod, following the company’s discovery of a way to let its customers play their downloaded tunes on Apple’s MP3 player. Apple criticized RealNetworks’ workaround, dubbed Harmony, as the ‘tactics…of a hacker,’ and warned in July that RealNetworks-purchased songs would likely ‘cease to work with current and future iPods.'”