While I was purposely being facetious about how easy it is, I'm sure some of your users know how to download a program and run it. It really isn't that hard, there's nothing going on that tries to make it hard or prevent it from getting removed. It's not a virus.
------------------
Not that anyone in their right mind would run smbd on an unprotected port or not behind a firewall, but it's still something that's pretty nasty. Patch already available.