Dlls and deployment

Hi, I have some components which I have purchased and I do have a
distribution license.

I use the dlls in my application by simply registering them via Visual
Studio.NET and therefore they are contained in the folder where the
application is installed.

My question is what stops people from simply grabbing these dlls from the
install folder and then referencing them in their own projects? I want to
protect the people who I purchased the dlls from and therefore ensure that
only my application can use the brought dlls. Can I do this?

Thanks in advance
Mark