Less than three months after Microsoft lost a key anti-trust case in the EU courts, it was back in the firing line Thursday as a Norwegian company announced that it had challenged the Seattle-based software titan before the European Commission, according to dpa. "Microsoft is abusing its dominant position... Opera has requested the Commission to take the necessary actions to compel Microsoft to give consumers a real choice," Oslo-based software developer Opera, which specializes in making the internet available to mobile devices, said in a press release. Microsoft reacted warily, saying that computer users already "have complete freedom of choice to use and set as default any browser they wish, including Opera, and PC manufacturers can also pre-install any browser as the default on any Windows machine they sell." "We will of course cooperate with any inquiries into these issues, but we believe the inclusion of the browser into the operating system benefits consumers, and that consumers and PC manufacturers already are free to choose any browsers they wish," a company statement said. A spokesman for the EU Commission, which oversees the implementation of EU competition law, would not comment on the case, but confirmed that the EU's executive had received the complaint. "We are going to study the complaint carefully, in particularly in the light of the case law established by the (European) Court of First Instance (CFI) in its ruling of September 17," he said. According to Opera, Microsoft is abusing its market position by selling its Windows operating system in combination with its Internet Explorer (IE) browser, thereby making it harder for other browser makers to sell their products. The Windows system is run on roughly 95 per cent of the world's personal computers. Microsoft is also harming competitors by not implementing widely- accepted Web standards in IE, so that non-Microsoft browsers that comply with those standards cannot view web pages written for IE as effectively as IE itself can, Jason Hoida, Opera's deputy general counsel, told Deutsche Presse-Agentur dpa. "In our eyes, this is an abuse according to settled European jurisprudence. Why should a consumer buy a competing browser, when they know that some Web pages will look 'incorrect' and when they know they will have to download and install the web browser themselves?" he said. Industry umbrella group the European Committee for Interoperable Systems - a key player in the earlier case, whose members include IBM, Nokia and Adobe - backed those accusations, saying in a statement that Microsoft was "depriving consumers of a real choice." "Browsers are the gateway to the internet. Microsoft seeks to control this gateway," ECIS chief counsel Thomas Vinje said. In its complaint, filed Wednesday, Opera asked the Commission to make Microsoft treat rivals fairly by either selling the Windows system without IE - a move known as "unbundling" - or by selling it with a number of different, non-Microsoft browsers included. It further asked the Commission to make Microsoft stick to the same international standards as everyone else, the statement said. In 2004, the Commission fined Microsoft almost half a billion euros (735 million dollars at current rates) after rivals complained that the US giant had tied its own media player into Windows, and had not allowed them fair access to codes which would have allowed their products to work effectively with Windows. Microsoft challenged that fine in the CFI, but on September 17 this year the court ruled in the Commission's favour, upholding both the initial fine and a further 280-million-euro penalty for failing to comply with the Commission's orders. "In our eyes, it's clear that the argumentation in that case should also apply to Explorer. We feel that we've got an important precedent set that we can use in this case," Hoida said.