Friend Request or Someone Trying To Sell Me Something?

How do I get on the "do not friend" list for all of this spam? I have not seen so many spammers as I have in the past two weeks. Whats up? They are also smart enough to leave my friends list immediately after they send their spam message. Don't get me wrong, I still want friends, and the ability to friend others I enjoy playing with, but maybe you have to play with that person first before they can friend you? Or maybe you have to be level 30 before you can send friend requests? I am sure that League is getting server stress from some of the account creation just for the sake of spamming others.