Any attempt to incorporate its own security software in Windows Vista, Microsoft's next-generation OS (operating system), could spark a new antitrust spat with Europe's top regulator, the EC (European Commission) spokesman Jonathan Todd warned yesterday.

Todd told Microsoft not to shut out security software rivals. Diversity and innovation could be at risk if Microsoft bundles its own security software with its dominant OS, he said.

Microsoft warned last week that Vista, due to launch early next year, may be delayed in Europe because of the regulator's concerns. The company said it hoped the EC would not demand the removal of important security features from Windows Vista in Europe.

"One of our principal concerns is that European consumers have access to the same new security features in Windows Vista as everyone else," said Erich Andersen, vice-president and associate general counsel for Europe. "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."

The spat over Vista's security features is similar to the disagreement over bundling Media Player, Microsoft's audio and video playing software, into Windows XP.

Two and a half years ago the EC found Microsoft guilty of foreclosing the market for audio and video players by attaching Media Player to its OS. It ordered the company to offer a second version of Windows with Media Player stripped out and fined Microsoft €497m (about £338m) for abusing its dominant position in the market.

The remedy Microsoft proposed is widely seen as a failure. Sales of the unbundled version of Windows, dubbed Edition N, are almost non-existent. Nevertheless, Todd said last week that the remedy's true value is as a precedent for future bundling issues that could arise from the launch of future versions of Windows, including Vista.

Microsoft was misleading people by implying that a possible delay to Vista's launch in Europe would be due to the regulator, Todd said. "It is not up to us to tell Microsoft what it has to do to Vista. The onus is on Microsoft to design its product in conformity with European competition laws, which it is well aware of," he said.