We often tell you about encryption. It's a system to protect you and your digital devices that companies like Apple and Google use to hide you from hackers and cybercriminals.
Encryption essentially scrambles your activity online, then hides it behind a password. It's so difficult to crack that Apple has said it can't even break into its own encrypted iPhones.
That's great for your security, which is why we tell you about it. The downside to encryption, and it's a big and controversial one, is that criminals can hide behind it, too. As it turns out, so can terrorists, like the killer California couple that murdered 14 people and injured many others last month.
The FBI recently told Fox News that it still hasn't been able to access the data inside the smartphones of the dead terrorists, Syed Farook and Tashfeen Malik.
The FBI, which also hasn't been able to find the couple's computer hard-drive, says there is an unaccounted-for 18 minutes of activity between the time Farook left his company's Christmas party and returned with his wife, Malik, and weapons.