Microsoft is to base the next version of its Passport service on open source Kerberos encryption, despite its controversial history with the protocol.

In using Kerberos, Microsoft aims to beef up Passport's security, which could pave the way for rivals to produce compatible competing products, rather than proprietary rivals, which would defeat the premise of Passport.

Passport is a critical part of Microsoft's Hailstorm web services strategy and is a central store of customer information. The service means that consumers can avoid having to re-enter personal details when visiting new websites.

Rivals such as AOL are thought to be working on competitors to Passport.

But the service has come under fire from privacy advocates who say its security is easy to bypass. They also question the wisdom of having such a large base of customer information under Microsoft's protection.

As a result, the software giant has changed Passport to require less information from users wishing to open an account, and last week turned to Kerberos, a portocol developed at the Massachusetts Institute of Technology.

Microsoft's track record with Kerberos is dubious, however, leading some industry commentators to doubt whether it is looking to make Passport truly compatible with rival products.