The European Commission (EC) is set to investigate whether Microsoft's .Net Passport system of collecting personal data from web surfers contravenes tough EC privacy laws.

Passport retrieves personal information from internet users and allows them to move between secure sites without the need to re-enter sensitive personal data.

News agency Reuters said it had seen a written response from the EC to a question from Dutch MEP Erik Meijer regarding the .Net Passport system.

Meijer had complained that .Net Passport does not enable users to unsubscribe, and yet if they do not subscribe they could find themselves barred from many key sites.

On 7 May the European Commissioner for the Internal Market, Frits Bolkestein, wrote: "The Commission is... looking into this as a matter of priority, in concertation with national data protection authorities, as regards the system's compatibility (or not) with EU data protection law."

Microsoft is currently engaged in ongoing anti-trust actions on both sides of the Atlantic. This probe has given the firm yet another headache.