Apple has claimed that RealNetworks has adopted the "tactics and ethics of a hacker" by developing software allowing iPod owners to download music from RealNetwork's RealPlayer Music Store.
RealNetwork's Harmony software tool allows music from the RealPlayer Music Store to be transferred to any music player, including Apple iPods.
Currently, iPod owners can only buy music online from Apple's own iTunes Music Store.
"We are stunned that RealNetworks has adopted the tactics and ethics of a hacker to break into the iPod," Apple said in a statement.
"We are investigating the implications of their actions under the Digital Millennium Copyright Act and other laws.
"We strongly caution Real and their customers that, when we update our iPod software from time to time, it is highly likely that Real's Harmony technology will cease to work with current and future iPods."
RealNetworks could not be reached for comment at time of going to press.
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