It looks like the official Dota 2 forum has been targeted by hackers as the site was apparently breached last month, with nearly two million user records accessed, which include email addresses, passwords, IP addresses and usernames.
News of the leak first appeared on Leaked Source, a site that gives users the ability to find whether their data is available online or not. According to the site, passwords for the forum were stored using MD5 hashing, which isn’t particularly effective by today’s standards. Apparently, more than 80 percent of the stolen passwords could be converted to plain text, so users of the Dota 2 forum should change passwords on other important accounts if they use the same password across multiple sites.
Source:
http://www.kitguru.net/gaming/security-software/matthew-wilson/dota-2-forum-hacked-around-2-million-users-affected/Full analysis:
https://www.leakedsource.com/blog/dotaTo see if you are affected:
https://www.leakedsource.com/main/