1,800 Minecraft accounts have been compromised, prompting users to change their passwords.
The 1,800 Minecraft accounts that have been compromised by hackers have leaked users' email addresses and passwords online.
This means that other people could use the leaked information to access those Minecraft accounts, and download the game to their own systems and devices. However, if any of the users that own the leaked information use the same email address and password for other, more sensitive, accounts (online shopping and banking, for example), it potentially means that they are compromised also.
Mojang have confirmed that the user account data has been leaked, but it wasn't done through hacking. The developers say it was done by other means - phishing.
Mojang say they have emailed everyone affected by the leak, and reset all the compromised passwords. If you haven't received an email from them about this they say "you don't need to worry," however we would suggest changing your password anyway, just to be safe. Change it over here.