Users of Google and Yahoo! have been duped into betraying their passwords to accounts.
However, they and Microsoft stress the hackers did not breach their databases, but conned email users into revealing information.
Microsoft has blocked access to thousands of Hotmail accounts in response to hackers plundering password information and posting it online
The Cyber thieves have are using tactics known as 'phishing' to trick users of free email services into revealing account and access information.
Yahoo says 'phishing' is an industry-wide problem.