Crypto mining in Android apps?!?

Received an email today which reads in part:

We noticed that you have published your app on Android Play Store/Apple App Store.We (REDACTED) provide technology services to enable app developers integrate REDACTED mining(a crypto currency similar to bitcoin, but very profitable to mine on general purpose devices like smartphones) within their app and monetize it. If your app is deployed on thousands/millions of devices, you can monetize it with REDACTED mining and earn really huge income.

I'm thinking that aside from being utterly unethical, this violates Google Play's developer regulations, and any app implementing such a system will rapidly be shut down and the account disabled.

Is this really a thing? Are people really integrating this kind of library with their apps? I've been out of the mobile dev game for a while now, and I'm a little behind on what's been going on.