macos – Why are files from macs often encrypted when copied to a hard drive and viewed from Windows?

Why are files from macs often encrypted when put on an external drive and that drive is plugged into a windows system?

I’ll explain what I mean ‘cos they don’t look encrypted at first sight, as you can open them..

but on closer inspection, they can show up green in windows explorer

and the windows cipher command shows then as encrypted, and their attribute properties show as encrypted.

I’m not the only person that has run into this, looking for example https://superuser.com/questions/58878/how-to-list-encrypted-files-in-windows-7 one poster writes “… I was cleaning up a external hdd and came across 150 files that where encrypted. So I wanted to know what and where they were as I do not use a encryption on my computers. Turns out it was from a few downloads that I can easily get. Or seeing “_MACOSX” folders on my pc. They are always encrypted.”

And they’re encrypted as if they were encrypted on the windows machine, in that they can only be viewed from that windows username @ that computer. As shown in the properties of the encryption in windows. And that user at that computer can decrypt them. But they somehow got encrypted like that. If that external drive were taken to another windows computer, then they can’t be read.

And i’m wondering what setting on OSX is causing that?