EC (European Commission) officials confirmed on Friday that they are examining informal concerns lodged by rivals against Microsoft's Vista OS (operating system), due to be launched by the end of this year.
"Several companies have expressed their concerns to the EC concerning Microsoft's Vista, but there are no formal complaints," said Jonathan Todd, a spokesman for the EC's top antitrust official, Neelie Kroes. "We are monitoring the situation, but there is no formal investigation".
Todd said the complaints are to do with the bundling of products into Vista, but declined to be more specific.
In a similar case in the US, Department of Justice officials are looking at Vista's bootup features and whether PC makers can customise the options presented to users when they switch on their PCs.
Todd also stressed that Microsoft should comply with the principles established by the EC's ruling of March 2004, which found that the company had abused its dominant position in the PC OS market, when "designing and implementing Vista".
On Wednesday Microsoft has to formally respond to a request from the EC to explain why it believes it has complied with the 2004 ruling. If the EC does not accept the company's arguments, it can hit Microsoft with a daily fine of €2m (about £1.37m).
The EC says the company has not yet provided sufficient documentation to allow rivals to develop products that can interoperate with its server software. Microsoft argues that the steps it has taken, including providing documentation, the offer of access to source code and free technical assistance, mean that it has fulfilled the Commission's demands.