I would be very careful downloading a .rar from an unknown source. Extracting could deliver a nasty payload to your computer. A legitimate instructional course could have been put up on a website. These exploits tend to occur later at nite on weekends when the forum is slow.
I completely agree. You don't want to download such files from an unknown source.
Why put into a .rar in the first place? Is this a PDF or a Word doc? Why not reupload the original file? I would like to read the hole lesson.