It has been revealed that the user information associated with more than 500 million Yahoo accounts was stolen in 2014. This data contains the usual details - Email, phone, security questions, date of birth and encrypted passwords.
This is the latest in a long line of massive data breaches that have previously involved companies like Adobe, LinkedIn, Dropbox and Myspace. There's been so many of these now that someone has created a website that you can use to check if your email address (and associated details) has been among the accounts compromised in any of these attacks.
Just enter your email address and / or username that you tend to use into that site, and it will check it against all known breaches for a match.
As ever, the advice for anyone affected is to change the password on any compromised accounts and any other accounts that shares this password. It is also advised that you enable two factor authentication whereever possible. For those that are unaware what two factor authentication is, we have dedicated this month's jargon busting blog to it.