More than 700 million email addresses, some including passwords have been leaked recently.
The data dump is believed to have originated in the Netherlands.
Cyber criminals allowed visitors to their servers to download their database without needing a username or password.
Australian Troy Hunt a computer security expert runs a website Have I Been Pwned (HIBP), which lets you check whether your account has been breached.
You can check if your account here.
If you are on the list, change your password immediately.