More than 6,000 inter-government and private sector messages were made public this week, including emails from ministries about sensitive issues, the Yomiuri Shimbun reported Thursday.
Officials from at least three ministries and a government agency inadvertently shared the contents of emails using the free Internet-based service provided by Google Inc., the newspaper said.
Information about January's negotiations for an international treaty on mercury, including details of meetings with foreign officials, were made public by senior officials within the Environment Ministry using the Web-based service.
Although not considered "top secret," the memos were not intended to be viewed by the public, a ministry spokesman said.
The ministry appeared to be putting the fault at Google's door, saying the Google Groups service "violates the ministry's information management regulations," the Yomiuri Shimbun said.
Google has declined to comment.
Users of Groups can participate in online discussions, using email or directly on the Web, but its default setting allows public access to all content.
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