How do I get rid of Yahoo Messenger Spam Invites?

I don't log onto messenger that often...only when I want to chat with my aunt because it's cheaper than calling. However, every time I log on I get 15-20 "friend invites" from a bunch of spam bots wanting me to add them to my list. I always hit ignore and I think I have over 100 of them in my ignore list alone. they just keep coming. I checked my settings and I have it set so only people on my list can send me messages...but how do I stop people I don't know from trying to add me on messenger? It's getting so annoying that I haven't been on to chat with my aunt in months!