Microsoft has appealed against the €280m fine imposed by the European Commission in July this year after the software giant failed to comply with the landmark 2004 antitrust ruling.
Microsoft was expected to launch an appeal against the fine, after insisting that it had met the EC's demands.
"As Microsoft said in July, we would appeal the fines imposed on the company at that time. The deadline for the appeal was 2 October," said a Microsoft spokesman, adding that the company has complied with the Commission's decision.
Under the 2004 antitrust ruling, Microsoft was forced to unbundle its media player from Windows XP and also give rival software makers fair access to Windows.
But there is still some debate over whether Microsoft has complied with the ruling. A media-player version of XP was launched last year, and Microsoft says it has now made its server interoperability protocols available to other companies.
The EC, though, isn't convinced — hence July's fine of €2m per day, backdated to December 2005. It could even be increased to €3m per day if the EC believes Microsoft is still failing to comply.
To confuse matters, the EC made its July ruling before Microsoft handed over its final piece of evidence. This documentation, codenamed Paddington, ran to 2,600 pages and is still being examined by the EC.
Microsoft is already appealing against the original 2004 ruling.
In turn, the EC has also turned its attention to Microsoft's next operating system — Windows Vista. It has been told by the security industry that Vista will be anticompetitive, but the Commission won't say how far its investigations have progressed. It is also refusing to give Microsoft any assurances before the OS is launched early next year.
The Financial Times reported this week that the EC is concerned about the encryption and handwriting recognition software that is slated to be included in the operating system.
Relations between Microsoft and the EC appear to be increasingly taut. One Commission insider told the Independent that "we can't break wind without them suing us", suggesting that Microsoft was trying to tie up the Commission in complicated legal battles for years.