The European Commission is to conduct another competition investigation into Microsoft after more complaints from the software giant’s rivals.

But, despite the apparent parallels with a case lost by Microsoft last September, the new claim may not be as similar as it seems.

The latest Commission investigation will go ahead following December’s allegations from Norwegian browser firm Opera that Microsoft makes it hard for rivals of Internet Explorer (IE) to run on Windows.

Opera wants the Commission to force Microsoft to remove IE from Windows, or to pre-install alternatives. The claim is backed by an industry group ­ the European Committee for Interoperable Systems (ECIS) ­ which includes IBM, Nokia and Oracle.

Ostensibly the chances of success look high. Last autumn’s decision concluded Microsoft was guilty of illegally bundling software into Windows, and imposed a fine of €778m (£589m).

“It is regrettable that despite the judgment of September 2007, Microsoft continues to use its desktop monopolies to restrict competition,” said an ECIS spokesman.

But the claim does not have universal support.

The Association for Competitive Technology, which represents more than 3,000 software suppliers, says Opera’s allegations are undermined by the widespread use of the Mozilla Firefox browser.

And lawyers stress that the law is designed to protect consumers, not to fuel threats between competitors.

Adam Collinson, partner at law firm Eversheds, said: “These cases should not be about difficulties faced by individual companies but about whether the consumer has been put at risk.”