And yes, that is a major defamation campaign led by Microsoft against the OP. And since MS even refuses to clarify their claim about the OP's wrongdoing, I imagine he would have an easy time in a court.
Ye, it tells bad actors how the detection system works.
They just don't want to because that costs more money than being a huge piece of shit does.
In fact, I'll go further. MS owns we an explanation why they are warning on any random site. Not only the site's owner.
[EDIT] My point is simply that somehow we manage in basically every other space to let those accused of wrongdoing know what we think they did that looked like wrongdoing, but somehow when it's an Internet giant calling the shots that's just impossible and waaaaah too hard and the sky would fall if they ever treated anyone with any amount of humanity and respect. I think it's grade-A bullshit and they've just figured out they can get away with being assholes at scale and no-one will make them stop.
It’s not just the internet. No company disclosed their fraud detection techniques.
But it doesn't matter. MS is the one telling to the entire world that his software is not reliable. They don't get to tell it all over the world without bringing some evidence.
"We're using our enormous market power to wreck your company and won't even tell you roughly the kind of thing we think is wrong" is so unacceptable it ought to draw an application of some kind of corporate death-penalty, if it's a pattern of behavior and not just a rare accident that goes against official policy. Certainly it's, all on its own, a strong argument that there shouldn't be companies this powerful in the first place.
Microsoft has no idea that you own the domain when you contact them, you are just a concerned party reaching out to them.. you could be the site owner, you could be the criminal that planted the payload.
Until it gets to the point where it is determined that you are the owner, they are correct to not give out sensitive information to random people that decide to e-mail them.