Google's privacy polices came under fire again on Friday regarding changes to its Gmail service, two days after it was fined by France for data protection violations.
Gmail users could soon receive messages from people with whom they have never shared their email addresses, following the latest in a string of moves to link Google's email service with its online social network, Google Plus.
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The change was revealed by Google Product Manager David Nachum in a post on Gmail's blog on Thursday. He explained that the pool of contacts available to Gmail users was being broadened to include connections on Google Plus, whose email addresses they might lack.
"Have you ever started typing an email to someone only to realize halfway through the draft that you haven't actually exchanged email addresses? If you are nodding your head 'yes' and already have a Google profile, then you're in luck, because now it's easier for people using Gmail and Google Plus to connect over email," said Nachum, who is based at the web giant's headquarters in Mount View, California.
"As an extension of some earlier improvements that keep Gmail contacts automatically up to date using Google Plus, Gmail will suggest your Google Plus connections as recipients when you are composing a new email," he continued.
Nachum said the changes would make it easier for Gmail and Google Plus users to connect, and that people were free to opt out of the new feature if they wished.
However, some privacy advocates said users should have been asked first whether they wanted their Gmail accounts to be linked to Google Plus in this manner, and that the feature should be opt-in rather than opt-out.
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Marc Rotenberg, a legal professor at Georgetown law school and director of the Electronic Privacy Information Center, told Reuters the new feature was "troubling."
"There is a strong echo of the Google Buzz snafu," he said, referring to the social networking service that Google launched in 2010. It was discontinued in 2011 following privacy concerns regarding the use of Gmail users' contact details to create social networks that were viewable by all.
It comes amid pre-existing concerns about the ability of Google Plus users to add somebody else as a contact without the consent of that person. By contrast, users of social network Facebook, for instance, must approve all "friend" requests.
The new feature will be rolled out over the next few days. Google said users would get an email with information and a link to the setting when the update was ready.
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In the U.S. however, Google is under pressure to monitor its social network more closely following allegations of inappropriate behavior by users. Lobbying group Consumer Watchdog has described Google Plus as a "virtual playground for online predators and explicit sexual content" and called on Google to ban offending users.
—By CNBC's Katy Barnato. Follow her on Twitter @KatyBarnato