I've always used MikTeX as the main LaTeX base to compile/write my
*.tex/*.sty/*.cls files, so I downloaded the specific version 2.9.4521-x64 on my first computer (running Windows 7 Professional); and then the file extensions mentioned above were correctly recognized by the OS, as it can be seen inside a generic folder:
There is a difference regarding the file type (
LaTeX Class and
LaTeX Style that recognizes automatically the derived extensions; and so on my first machine I've had no problems at all.
The problem rised when bought a new computer, same OS, and installed the same version of MikTeX; then when I looked back on the same folder the file extension for class was no more recognized correctly by Windows:
Here the file type that describes a class file is recognized as
CLS file, and not
LaTeX Class, because I had to manually connect the program that will be able to read the extension, as it can be seen by the different icon appeared in the aforementioned image.
I know it may seem as a not-so-dramatic issue, but I don't know what is causing it, and since there is an image proof surely something must have happened.
EDIT: As karlkoeller suggested, removing the current TeXworks version from the MikTeX distribution and installing a brand new one generates this output:
So it looks like I'm back on where I started.