Chief Executive Mark Zuckerberg described the incident as a “really serious security issue"
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Yahoo, now part of Verizon Communications Inc, said on Tuesday that an investigation showed all 3 billion of its user accounts were affected in a 2013 data theft, tripling its earlier estimate of the largest breach in history.
Yahoo has begun warning individual users that their accounts with the service may have been compromised in a massive data breach it reported late last year.
The TOR Project is advising users to upgrade to a new version of the software following a hack that compromised three of its servers.