[Spooky23]

Especially when you consider that the common practice on Windows is to use less secure alternatives like Putty that are high risk for trojans.

Unless they are on smartcards, there's always a way to compromise keys like this.

[TheRealPomax]

There isn't even a "compromised" situation here: this is literally how it's meant to work.

Admin accounts have access to everything, whether that's the registry, or a subdir in your user profile dir. That's the whole point of admin rights. Whether your private key is in a file in an .ssh dir or stored in the registry, admins can always get to them.