Unfortunately, this does happen in SL, and is not just with KittyCats. Block and mute are your best pair of claws.
I think it happens because for every hundred or even thousand people spammed, someone will pay a visit and possibly make a purchase. That is a win for some people, I guess.
Still, it helps to talk about it, because as you see, you are not alone. Sounds like this person was spamming out to a group, which isn't surprising. They will just make a new alt, rinse, and repeat. Ugh!
