(United Press International) Attackers now own an undisclosed number of Yahoo! Mail usernames and passwords, stolen from a third-party site, the Sunnyvale, Calif., Internet giant said.

As a result, Yahoo! will now require affected users to change their passwords and use a one-time second sign-in verification to re-secure their accounts, Yahoo! Inc. Senior Vice President Jay Rossiter wrote in a blog post.

“We regret this has happened and want to assure our users that we take the security of their data very seriously,” Rossiter said in the blog.

He did not say when the breach occurred, other than “recently.” He called it a “coordinated effort” but did not say which third party was involved.

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