Two Symantec engineers will visit Brussels next week to discuss the antitrust threat posed to their company by the upcoming Windows Vista OS (operating system).

Vice-president for consumer engineering Rowan Trollope and a senior engineer in the technology strategy office, Bruce McCorkendale, will press their case to the European antitrust regulator, the EC (European Commission).

The EC has warned Microsoft about the possible impact on competition of Vista's built-in security software. The regulator fears that including a sophisticated antivirus program could have a similar effect to the bundling of Media Player with Windows XP.

Two and a half years ago the EC ruled that the bundling of Media Player into Windows was anticompetitive and ordered Microsoft to launch a second version of Windows without Media Player. It also fined the company nearly €500m (£335m).

Meanwhile, Adobe has told EU regulators that Microsoft should be banned from bundling in free competing software for reading and writing electronic documents into Vista, according to a report in The Wall Street Journal Europe.

The paper cites unnamed people familiar with the situation.

Adobe and Symantec lobbying moves will come as no surprise to the EC. Competition commissioner Neelie Kroes wrote to Microsoft in March expressing concern about Vista's impact on competition, and cited the computer security and document reader and writers sectors as examples of where Microsoft's bundling strategy might pose competition problems.

However, earlier this week Kroes insisted she wasn't calling for Microsoft to launch Vista without any security system.

"I have seen it suggested that the EC may seek to prevent Microsoft from improving the security of its operating system. This is categorically not the case," she wrote in a letter to the Financial Times newspaper.