Dirty pictures on daughter's phone

Hi all,Well, after years of lurking I finally have a reddit name and am making my first post.I'm a single dad with two girls, 14 and 16. My wife passed a few years ago and I have not remarried or even dated seriously. My income is more than sufficient to support my kids, and they are independent girls who have been doing well in school and activities.I am currently in a dilemma over the topic of sex. I dropped my 14 year old off at soccer practice last night, and noticed that she had left her phone in the car. Thinking nothing of it, I took the phone home with me. After I got home and as I was putting her phone on the kitchen counter, I saw a notification from her boyfriend in which he requested oral sex this weekend when she has a sleepover (he is one of her friend's brother.) I was concerned and looked through the rest of her phone (it's a rule in our house that the passcodes are our birth dates) and found dozens of sexual pictures to varying extents that she has been sending not only her boyfriend but other guys in her phone contacts and kik, I assume. Some were "innocent" bikini pictures and such; others were of her naked. Not knowing what to do, I turned her phone off, and told her later that I had done so since the battery was low. Lame excuse, I know, but I think it worked.My question is, how do I address this? From the texts I saw between her and her boyfriend, it appears that they have not had full-blown sex. I am grateful for that, but it's more of a concern to me that she is sending so many pictures out to her peers. Blackmail from one of them is a possibility, as is them sharing her pictures with yet more people. I have thought about talking to her sister about it and seeing what she suggests, but I'm worried that her sister's loyalty might be more to my 14 year old than me, and that our communication won't be confidential. There's also the possibility that my 16 year old also engages is the same behavior, which I would have to deal with too.Help me out, parents of reddit. What should I do? via /r/Parenting http://ift.tt/2juZE3b