Update Google has confirmed that Gmail has also been targeted by an "industry-wide phishing scheme" which first hit Hotmail accounts. Yahoo! and AOL are also reportedly affected.
Hackers used fake websites to gain the login credentials attached to various webmail accounts. The attack emerged after a list of 30,000 purloined usernames and passwords was posted online. These leaked details reportedly referred to Gmail, Comcast and Earthlink accounts.
A second list containing webmail addresses and passwords referring to Hotmail, Yahoo, AOL and Gmail also surfaced online. Some of the addresses on this list were old and fake, but at least some were genuine, the BBC reports. Both lists have been taken offline, so are no longer directly accessible.
The search engine giant confirmed that an unspecified number of accounts were compromised, adding that it had reset the passwords of the compromised accounts.
"We recently became aware of an industry-wide phishing scheme through which hackers gained user credentials for web-based mail accounts including Gmail accounts," a Google spokesperson told the BBC.
"As soon as we learned of the attack, we forced password resets on the affected accounts. We will continue to force password resets on additional accounts when we become aware of them."
In a statement sent to El Reg in response to out inquiries, Yahoo confirmed that an unspecified number of Yahoo webmail accounts were on the leaked list. It couldn't confirm how many of the profiles were genuine.
We are aware that a limited number of Yahoo! IDs have been made public.
Online scams and phishing attacks are an ongoing and industry-wide issue and Yahoo! takes great effort to protect our users' security. We urge consumers to take measures to secure their accounts whenever possible, including changing their passwords. We also encourage our customers to review resources that provide guidelines on email safety.
Earlier 10,000 Hotmail IDs and passwords were posted online at Pastebin, a site more commonly used for developers to share code. It's unclear whether this list was connected to the latest password harvesting scams.
This list has also been taken offline, but it appears that the horse has already bolted. "Making the breach public so soon after the attack occurred has allowed unethical hackers to access the passwords very easily, even though they were deleted a couple of days ago at the request of Microsoft," said Neil O'Neil, a digital forensics investigator at secure payments firm The Logic Group.
Rik Ferguson, a security researcher at Trend Micro, said that the security firm had begun detecting spam sent through these compromised Hotmail accounts.
As many as two in five people use the same password for every site they use. That means access to a webmail account gives hackers a head start in accessing online banking or PayPal accounts linked to the same address.
Underground bazaars and carder forums are full of sales of these more sensitive login credentials. Email addresses have sold alongside purloined credit card numbers and online bank accounts for months if not years on such black market forums.
Seen in that context the webmail phishing is not as shocking as early mainstream reports might suggest. The combined incidents serve to further illustrate the importance of password security. Using a different, hard-to-guess password on every site is a very good start in this direction. ®