A trio of computer security researchers say they've successfully compromised Microsoft's CardSpace, a technology intended to strengthen the security of personal information on the Internet.

CardSpace ships with the Windows Vista operating system. It works in concert with a browser when someone uses a Web site that asks for information such as an address or a credit card number. That personal information can be stored on the user's computer or with a third-party identity provider.

CardSpace keeps a set of virtual ID cards on the user's computer. When a Web site asks for information, the user picks one of the cards. "Self-issued" cards store identity information on a user's PC, while "managed" cards are stored by an identity provider.

When logging into a Web site, the user can ask the identity provider to vouch for them, which saves having to remember a slew of different passwords, a concept known as single sign-on. Rather than directly receiving the personal information, the Web site gets a token from the identity provider, adding an additional layer of security to a Web transaction beyond SSL (Secure Sockets Layer) browser encryption.

The researchers, from the Horst Gortz Institute for IT Security at Ruhr University in Bochum, Germany, have shown it is possible to intercept the authentication token from CardSpace. The hacker could then use the token to gain access to the other site or transmit sensitive information to that site.

Microsoft is hoping CardSpace will reduce problems plaguing Internet users such as identity theft. The company has also pledged to integrate CardSpace with OpenID, an open-source standard with the same goals that has been implemented in part by companies such as Yahoo. However, Web sites have to be designed to work with CardSpace and OpenID, and so far, neither is widely used.

The attack against CardSpace involves directing a user to a malicious Web server. In their explanation, the attack involves modifying the victim's DNS (Domain Name Server) settings -- another trick known as "pharming" -- and direct the person to the malicious Web server, which is then able to grab the authentication token.

So far, the method remains proof-of-concept and has not been used to attack people. But that could change, the researchers said.

The attack can be easily replicated, according to the Horst Gortz Institute. The researchers "conclude that it is realistic to expect attacks against CardSpace soon in the wild."

Microsoft officials said they are looking into the research.

The research was done by two IT security students, Sebastian Gajek and Xuan Chen, and Jorg Schwenk, a professor and chairman of Network and Data Security at the institute.