Personally, I use the SpamMeNot adddon.
Set it and forget it really. Set the level of person you don't want
whispering you and leave it. And it also blocks random/macro group
invites as well, including the program itself sending you a whisper
stating the level and name of the inviter. Sets the 'human response'
barrier that it auto-refuses and then if there IS a human on the other
side, you can choose to allow them to invite you or they can just
Invite again.
It's a bit high and mighty but it sets the bar straight for privacy
imo.
