I'll try this one time and then its up to people to decide if they want to leave the cave...
But on Steam they have a beta for Steam Communites. If someone sends you an invite to join a community and you're not in the beta the invite says its from "unknown".
So, if you want to join the beta, when you log into steam look on the main page for a button, about 2/3s down that says something like "Join beta." I'm not at home so I can't recall exactly where it is, etc...
But, the point is, no one is hacking you. And, if you join the beta the invites will work correctly.
Good luck.