A hacker has stolen tens of millions of accounts from over a thousand popular forums, which host popular car, tech, and sports communities.
The stolen database contains close to 45 million records from 1,100 websites and forums hosted by VerticalScope, a Toronto-based media company with dozens of major properties, including forums and sites run by AutoGuide.com, PetGuide.com, and TopHosts.com.
The company didn't outright confirm the breach, but said it was investigating.
"We are aware of the possible issue and our internal security team has been investigating and will be collecting information to provide to the appropriate law enforcement agencies," said Jerry Orban, vice-president of corporate development, in an email.
"We believe that any potential breach is limited to usernames, user IDs, email addresses, and encrypted passwords of our users. In addition, we are reviewing our security policies and practices and in response to increased Internet awareness of security-related incidents, including potential incidents on our communities, we are implementing security changes related to our forum password strength and password expiration policies across certain forum communities."
In a sample given to ZDNet, the database shows email addresses, passwords that were hashed and salted passwords with MD5 (an algorithm that nowadays is easy to crack), as well as a user's IP address (which in some cases can determine location), and the site that the record was taken from.
The group said in its blog post that it was "likely that VerticalScope stored all of their data on interconnected or even the same servers as there is no other way to explain a theft on such a large scale."
Despite a push in recent years for stronger encryption and fixing security flaws, the forums thought to be affected by the breach fell far behind industry security norms.
A cursory search of the list of domains caught up in the hack revealed that none of the sites we checked offered basic HTTPS website encryption, which would prevent usernames and passwords from being intercepted.
Many of the forums ran versions of vBulletin software dating back to 2007. Most were running software versions that were easily exploitable by hackers with known vulnerabilities. A blog post from security reporter Brian Krebs from 2013 showed that older versions of the vBulletin forums that were vulnerable could be easily searched with readily-available attack tools.
It's not clear who carried out the hack. A LeakedSource group member said it was "not related" to the recent hacks against MySpace, LinkedIn, and Tumblr.
As of Tuesday, the company has not made any public statement in relation to the hack.
Unlike in other recent other breaches, this data does not appear to be for sale on the dark web -- for now.