Apple is facing a legal battle over a key contested patent that could threaten a range of its products, including its massively popular iPod music player.

Fresh from a $60 million legal victory over Microsoft, Burst.com, an American firm that specialises in audio and video software, has now alleged that Apple has infringed four of its patents in its iTunes online music store, its QuickTime media products, and the iPod.

Burst.com brought the case in federal court in San Francisco this week after negotiations between the companies over the disputed patents, which date back as far as 1988, broke down earlier this year.

The company is seeking an injunction that would prevent Apple from using the technology covered by the patents unless it paid a "reasonable royalty".

The action follows a pre-emptive suit filed by Apple in January, which sought a declaration that Burst’s patents were invalid.

But Burst's track record could give Apple cause for concern as the tit-for-tat legal battle escalates. Last year, it won a $60 million settlement from Microsoft after a dispute over some of the same patents.

The disputed technology in each case allows audio and video content to be transmitted at a faster rate than its playback speed – a key feature for online music download services.

"We have a responsibility to protect our patents and to seek a fair return for the many years and tremendous investment that we have made in developing Burst technology and patents," Richard Lang, the Burst chairman and chief executive, said.

In its January filing, Apple claimed it had been threatened by Burst during negotiations, and seemed to suggest the smaller company was acting as a litigious "patent troll", eager to cash in on protected technologies.

"In late 2005, in at least one written communication, Burst.com’s attorneys threatened litigation against Apple," Apple said. "Apple denies that any of the patents in [the] suit are or have been infringed by Apple and disputes their validity."

Burst, which has reportedly added significantly to its legal team in preparation for a potential courtroom showdown admitted in subsequent documents that it had sought to "aggressively defend its intellectual property rights" but insisted that it ‘sincerely hopes that it can avoid litigation by coming to a mutually agreeable resolution of these patent issues with Apple.’"

The latest action is the latest in a string of recent legal wrangles to overshadow Apple.

The group already faces the prospect of action from French lawmakers that could force it to open up the current closed link between iTunes and the iPod or cease offering the online music service in the company.

In Britain, Apple faces a suit from Apple Corps, the Beatles record label, which is seeking an injunction against the use of the Apple apple name in connection with the computer company's music products and services.

Do patent wrangles like this pose a greater threat to companies or consumers? Have your say here.

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