European Union officials warned Microsoft Corp. on Tuesday not to shut out rivals in the security software market as the company plans to upgrade its new Vista operating system with its own security features.

EU spokesman Jonathan Todd told reporters that the European Commission is ready to give guidance to Microsoft concerning its new Vista product, but added that it was up to the U.S. software maker to accept and implement its responsibilities as a near monopolist to ensure full compliance with EU competition rules.

Microsoft, meanwhile, warned EU regulators to avoid attempting to block the in house security upgrades it is making to Vista.

We are concerned that (regulators) might require the removal of some of the security features we've demonstrated, Erich Andersen, Microsoft's associate general counsel told reporters. We want to launch Windows Vista in a fully lawful manner and we want to avoid regulatory decisions that could increase security risks for European consumers.

Andersen told reporters the company was adding a pre installed firewall in Vista.

Todd said the Commission understands Microsoft's wish to make Vista more secure. But he added that the EU head office believes computer security depends on diversity and innovation in the field of security software, (and) such diversity and innovation could be at risk if Microsoft was allowed to foreclose the existing competition in the security software markets.

He said that bundling its own security product as part of Vista, its own dominant operating system ... would ultimately harm consumers through reduced choice and higher security risks.

Microsoft has threatened a delay in the launch of its next generation Vista operating system in Europe because of the new standoff with EU regulators.

EU antitrust regulators said last week it was not up to them to give Microsoft a green light to launch its new desktop software in Europe after Microsoft complained that it could face delays unless the EU told it what it must do to avoid antitrust problems.

EU Competition Commissioner Neelie Kroes wrote to Microsoft CEO Steve Ballmer in March, pointing out possible issues with Vista's integrated Internet search, digital rights management tools used to protect copyrights and software that would create fixed document formats comparable to Adobe Systems Inc.'s Portable Document Format, or PDF.

There is no formal investigation into Vista but Microsoft is still embroiled in a long running legal challenge to the EU's 2004 antitrust order that found it broke competition law and fined it a record euro497 million.