A Yahoo representative has confirmed that the data published Thursday was indeed some 450,000 names and passwords for Yahoo and other companies.
"We confirm that an older file from Yahoo Contributor Network (previously Associated Content) containing approximately 450,000 Yahoo and other company users names and passwords was compromised yesterday, July 11," Caroline MacLeod-Smith, Yahoo's head of consumer PR in the UK said via e-mail. "Of these, less than 5 percent of the Yahoo accounts had valid passwords. We are taking immediate action by fixing the vulnerability that led to the disclosure of this data, changing the passwords of the affected Yahoo users and notifying the companies whose users accounts may have been compromised. We apologize to all affected users. We encourage users to change their passwords on a regular basis and also familiarize themselves with our online safety tips at security.yahoo.com."
The group of hackers calls itself "the D33Ds Company" and claims to have hacked into the database by exploiting an SQL injection vulnerability found on a Yahoo subdomain. They published a list of over 453,000 log-in credentials on the Internet that were allegedly stolen from a database associated with an unnamed Yahoo service.
Even though the hackers did not name the affected Yahoo subdomain, Dave Kennedy, the chief executive officer of security firm TrustedSec, speculated, based on a host name found in the leaked data, that the service is Yahoo Voices, a library of user-generated content formerly known as Associated Content from Yahoo.
The leaked information includes MySQL server variables, names of database tables and columns, as well as a list of 453,492 e-mail addresses and passwords in plain text.
The exposed log-in credentials don't only include yahoo.com e-mail addresses, but also e-mail addresses from other public and non-public email providers. (See also "Create a Different, Secure, Easy-to-Remember Password for Every Site .")
Hackers Mock Yahoo's Security
"We hope that the parties responsible for managing the security of this subdomain will take this as a wake-up call, and not as a threat," the hackers said. "There have been many security holes exploited in webservers belonging to Yahoo! Inc. that have caused far greater damage than our disclosure. Please do not take them lightly."
"The subdomain and vulnerable parameters have not been posted to avoid further damage," the hackers said in their release notes.
An analysis of the data by Anders Nilsson, chief technology officer at Eurosecure, antivirus vendor ESET's distributor in Scandinavia, revealed that the most common domain names for the leaked e-mail addresses were yahoo.com, gmail.com, hotmail.com and aol.com.
The most common password was "123456" -- used by 1666 users -- followed by the word "password" -- seen 780 times. In addition, "password" was used as a base word for 1373 passwords.
If someone's log-in credentials are leaked, there isn't much they can do except to change their passwords as soon as possible, pressure the responsible service provider into improving its security and consider moving to a safer service, David Harley, a senior research fellow at antivirus vendor ESET, said in a blog post on Thursday.