Microsoft says it is on track to launch Windows Vista simultaneously worldwide. Less than a month ago it warned that antitrust problems could delay the launch in Europe and South Korea.

A delay in one country or region would have serious consequences for software developers, computer manufacturers and retailers there. It would also create complications for Microsoft, which has always rolled out new versions of Windows simultaneously around the world in the past.

Steve Ballmer, the company's CEO, confirmed the global launch of Vista in a telephone conversation with European competition Commissioner Neelie Kroes late on Thursday. The new operating system will go on sale to large computer manufacturers next month and to the general public in January.

In the statement issued Friday Microsoft said it had made changes to Vista to address the concerns the commission has expressed about the new operating system. It has also addressed the concerns of South Korea's Fair Trade Commission, Microsoft said.

"We are excited to bring the security enhancements and innovative new features of Windows Vista to our customers and partners around the world, and we are committed to adhering to local law in every region of the world," Ballmer said in the statement.

Until now Microsoft has resisted pressure to change Vista. Last month it accused the European Commission of not giving it clear enough guidance on whether Vista would pass muster under European antitrust law.

It also unveiled research that showed that hundreds of thousands of jobs in the European IT industry were at stake if Vista's launch was delayed. Also last month, members of the European Parliament understood to be sympathetic to Microsoft's position wrote to Kroes warning her of the harm she would be causing to European companies if she forced a delay in Vista's European launch.

The Commission stood its ground, insisting that it wasn't up to the regulators to give Vista the go-ahead before its launch. It repeated this message on Friday. "The Commission has not given a 'green light' to Microsoft to deliver Vista. Microsoft must shoulder its own responsibilities to ensure that Vista is fully compliant with competition rules and in particular with the principles laid down in the March 2004 Commission anti-trust decision concerning Microsoft."

Many of the problems with Vista identified by the Commission echo the issues that resulted in the antitrust ruling two and a half years ago. It alerted Microsoft to five potential antitrust problems in March, which were addressed in changes incorporated into the new operating system over the past few months.

Last month the Commission pointed to three remaining problems, concerning Microsoft's plan to bundle with Vista an internet search engine, security software and a fixed document format similar to Adobe's.

In 2004 the Commission found Microsoft had acted anticompetitively in bundling its Media Player into Windows XP and ordered the firm to release a second version of Windows without the program.

Symantec, one of the leaders in antivirus software, recently embarked on a massive public relations offensive, claiming that Microsoft was effectively shutting it and other security software specialists out of Vista.

Then Microsoft changed its tune. Two weeks ago it addressed Symantec's main concerns by agreeing to allow non-Microsoft security products to access the heart of the Windows operating system.

It also agreed to ensure that Windows Security Center, the new security function, will not send an alert to a computer user when an alternative competing security console is installed on the PC in order to avoid confusion and irritation among computer users.

In the area of search, Microsoft changed Vista to allow people to choose their own search engine and make it their PC's default internet search tool.

In the area of fixed document formats, Microsoft agreed to the Commission's demands that its new fixed-layout document format, called the XML Paper Specification, should be scrutinised by an independent standards-setting organisation. It also agreed to change the licensing terms to make its format more available to other software developers.

"We understand that the European Commission doesn't give a green light to a product before it is launched, and that it is a company's obligation to be in compliance with antitrust law," said Brad Smith, Microsoft's most senior lawyer, in a conference call Friday.

"Having made the changes we were advised to make, we are confident Vista is in compliance," he added.

The Commission said in a statement that it will "closely monitor the effects of Vista in the market", and will examine any complaints the new operating system may provoke "on their own merits."

(Peter Sayer in Paris contributed to this story.)