I have a competitor site that is doing blackhat SEO. My question is if I report them to google, would they keep it anonymous or would they share my details? Also, has anybody here received any notice here from Google penalizing the site? What's the message they send you?
How to report? Can I report, for example, spam posts / links? What threatens the reported site? If I do not like someone, I will create such posts myself, and then I will report it (I know, it's not nice, but it's worth knowing) - will it also hurt reported website? How it's working?
I think you need not tell Google anything. Google is enough smart for understanding anything, if your competitor is applying black hat then Google will definitely penalize them, but keep focusing on white hat practice only.
You will stay anonymous while you report. On the other hand make sure to disavow links as you see them in webmaster. Google is various algorithms that understand those kinds of activities & it won't harm your site.