The curse of needing a separate login and password for different websites may soon be a thing of the past.

Yahoo!, the internet giant, has announced that it will put its weight behind a system that allows users to have a single sign-on for any website which requires registration.

From the end of the month, Yahoo!'s 250 million users will be able to apply for an OpenID, an identity that allows websites to share login information in order to reduce the hassle for the user.

The system works by first asking the user to log in with one site, known as an OpenID provider. When other participating websites are visited, they effectively ask the first site whether the user is who they say they are. If the first site - for example Yahoo! - provides authorisation, the person is logged in.

The backing of the Yahoo! - the most visited site in the US and the third most popular globally - will provide a significant boost to OpenID, which has 130 million subscribers but has so far failed to attract any of the web's biggest names.

So far AOL is the largest brand to have signed on. Google uses the system in a limited capacity on its Blogger service.

Raj Mata, director of memberships at Yahoo!, said: "This is another step forward for the open web. It is a hassle for users to have to log in to different sites. Often you have to register an account with a site - which you won't remember - just to post a comment. We think this reduces the barrier to entry."

Mr Mata said that Yahoo! would initially enter the scheme only as a provider, meaning that Yahoo! will not trust other sites to log in its own members to their e-mail and other accounts.

Conversely, Yahoo! members who sign up for an OpenID will be able to log straight into other sites which participate.

OpenID has come under criticism from some security experts, who say there is the potential for consumers to be tricked into entering their log-in into a site that is not genuine, as happens in phishing scams.

"The whole thing is fantastically dangerous until you can introduce cryptographic methods which ensure that the whole procedure is not phishable," Ben Laurie, an independent security expert, said.

Microsoft is developing its own system for universal logins, called Cardspace, which requires a greater degree of information about the user and also employs cryptography, which some experts believe is more safe.

Yahoo! said that the latest version of the OpenID protocol addressed all the relevant security issues and that there were now "background checks" which provided assurance a site a user was redirected to to enter their 'OpenID' was authentic.

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