Pamela Casey, the district attorney for Blount County (population 58,000), published the warning on her office's Facebook page. It has attracted 2.4 million views since Tuesday (Sept. 1).
Casey showed parents how to identify the app, Private Photo (Calculator%), on their children's smartphones. The app appears to be a simple calculator, but it unlocks a private photo album when users punch in a special code.
She urges parents to look for Private Photo app on their children's phones and demand to know their password if they find it.
Previously, Casey made videos urging parents to talk to their children about the danger of sexting.
The app is actually one of several that set up private photo albums under the guise of a calculator. Of course Snapchat has also become widely popular with its erasable photo messaging app.
Some of the comments on Casey's Facebook page suggested her warning is somewhat late to the game, although many other comments were from parents thanking her for the heads up.