Steam users have been advised to change their passwords and reset Steamguard as Valve has patched the Heartbleed vulnerability. The service experienced several issues with developer passwords being compromised and the name of some games (Dino D-day, Call of Duty: Black Ops 2, and South Park: The Stick of Truth) changed to warning messages about resetting developer passwords.
The Heartbleed bug is a vulnerability in the encryption that secures OpenSSL that allows hackers to retrieve information from the server without leaving a trace. Popular webcomic XKCD has provided a relatively accurate example of how the exploit is used to read the contents of a server.
Steam has also had to deal with White hat hackers gaining access to developer accounts to warn them of the vulnerability in the system. SteamDB has indicated that a patch has been installed to correct the vulnerability, although users are still advised to change their passwords for security reasons.