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Microsoft defends Hotmail's cookie requirement

Log out block 'good for security'

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Microsoft has said its new policy of requiring users to accept third party cookies to log out of Hotmail improves security.

We reported the change, which was applied earlier this month, yesterday.

Some readers who contacted El Reg said it raises the risk that accounts will be compromised on public machines, while others who do not allow third party cookies simply found the error message when they tried to log out irritating.

Angus Logan, the product manager for Windows Live ID, told The Register the use of third party cookies has two benefits.

"We write our cookies to multiple domains to give users a good experience with single sign-on, so they can be authenticated to multiple sites (e.g. MSN, Xbox Live, Windows Live, Bing) at once without having to retype their password," he said.

"[It also] helps protect user security, by separating the authentication cookies that are used for different services. If a cookie in one domain is compromised, it means that user assets in another domain won't be compromised."

Microsoft now uses third party cookies - more controversial than first-party ones because they allow tracking across multiple websites and services - for log out to check whether users are logged into more than one of its web services.

"During sign-in, we redirect to the right domain so that the cookies can be written in first-party context," Logan said.

"It's only during sign-out, where we need to clear cookies from potentially many domains that we have login.live.com clearing cookies in other domains via the invisible GIF solution*. We are actually removing cookies in this scenario, but it's interpreted by browsers as using third party cookies."

Hotmail users who don't accept third party cookies must now shut down their browser to log out. ®

*There's more info here.

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