Websites and Internet users are scrambling to deal with a serious security bug that could put personal information at risk.
It's called "Heartbleed."
It affects a widely used program that is used to encrypt data on sites like Google and Facebook.
The bug went undetected for more than two years.
Although there is a fix now, experts say email accounts, credit card information and other sensitive data could already have been compromised.
They suggest that once you know that a website has patched the vulnerability, you should then log in and change your password.