I'd discuss it with her once

Casadena

Dear Prudence,

I am the proud mother of a beautiful 22-year-old daughter. She’s been a stellar student—she graduated from an Ivy League school—and a terrific kid, and we have a great relationship. She’s living back at home after completing college and working part-time as she prepares to apply to law school. Recently, I forgot something I needed and hurriedly ran into the house. As I went by her room I saw her naked and performing sexually on camera. When we spoke about it later she didn’t seem embarrassed and explained that while it was not any of my business, it was something that she and her boyfriend do frequently when they cannot be together physically. I’m not proud of this, but the next day while she was out I sneaked a peek at her computer. I found literally hundreds of explicit pictures of my daughter with men and women, and I do mean explicit. Knowing that I violated her privacy, I’m a little apprehensive to come clean and tell her what I found while snooping on her personal computer. But I want to find out more about her extracurricular activities and express my concerns that theses types of things could have a way of coming back to haunt her later in life.

—Freaking Out Mom

short+sassy

Oof!  The daughter should have kept her door closed, just to be on the safe side., but it's too late now.

The mom shouldn't have gone snooping in her computer, knowing she would probably find pics/videos that she did not want to see.  That's her punishment.  But photos on the daughter's computer aren't proof they are online anywhere.

I think it's better to have a general discussion about the dangers of sending explicit photos/vids to others or "performing" for someone who could be recording her.  That these can come back to haunt her even years into the future.  That stays within the "story" her daughter told, while still getting the point across.  

MyNameIsNot

I would not tell my 22 y/o daughter that I went snooping in her computer, but I never would have done that in the first place. She's not a child. 

What to say would have a lot to do with what conversations we'd had in the past and generally her personality. Daughter is 22. Sexting, revenge porn, snap chat, only fans, etc have existed since she was in diapers. Unless she's particularly naive and LW failed as a parent, she should have an understanding of the risks here. Maybe a broad "are you being safe?" is in order, but I wouldn't go into this assuming she has no idea what could happen.