RICHMOND, Va. (AP) — As a member of the secretive Senate Intelligence Committee, Sen. Angus King has reason to worry about hackers. At a briefing by security staff this year, he said he got some advice on how to help keep his cellphone secure.

Step One: Turn off phone.

Step Two: Turn it back on.

That's it. At a time of widespread digital insecurity it turns out that the oldest and simplest computer fix there is — turning a device off then back on again — can thwart hackers from stealing information from smartphones.

Regularly rebooting phones won't stop the army of cybercriminals or spy-for-hi...