Search engine Google has revealed that the files of some Google Docs users have been shared with unauthorised users.

Google said a flaw in the software meant that if a user selected multiple documents and changed the sharing right, some files were marked as 'collaborative' rather than 'private'. This means other users of the service could access and edit the documents.

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The search engine said in a blog that the flaw, which it thought only affected 0.05 percent of its users, has now been fixed. "We've identified and fixed a bug where a very small percentage of users shared some of their documents inadvertently".

"The inadvertent sharing was limited to people with whom the document owner, or a collaborator with sharing rights, had previously shared a document."

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Google said it did not affect spreadsheets created in the software.

"We're sorry for the trouble this has caused. We understand our users' concerns (in fact, we were affected by this bug ourselves) and we're treating this very seriously. We hope this explanation provides greater clarity," added Google.

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