Readers here are all very likely to appreciate some links alongside statements, cause really this is a sensitive topic. Both statements need certain context as it seems it’s not the universal understanding of what goes on and how often.
Not sure it can be proven with citations but it's well known that process injection is widely used on Windows. GPU drivers are known to do it. Utilities have historically often injected code into Explorer. Raymond Chen has written in the past about this problem and how hard it made it to evolve the platform.
For code injection into applications that don't load third-party DLLs as plugins, see, e.g., Microsoft's (unsupported) toolkit for runtime API interception:
You install tortoiseSVN or something similar, look at explorer.exe process or any process that use a standard "Open File" widget, and you will see some dll from the utility loaded by the process. (Easy to see with process explorer from sysinternals)
I think tortoiseSVN and consorts are "just" a shell extension, though, which is an officially supported concept, even if that means that potentially any random software using the standard file dialogues ends up loading your DLL, too.
Yeah. That really doesn’t need to be from the store.
I really hate going through the Apple Store to download Xcode. We all know how to download software. I’d rather go through a dev portal than a consumer portal.
I'm still waiting to hear about a kernel-level exploit that starts with Visicalc or similar.