Why do i keep getting i.ms were the person only buzzes me but doesn't say anything?

ive gotten about 15 in the last 2 days they don't say anything or post any links and they don't have links to in there profile like normal bots,ive been reporting them as spam and brushing them off until today when i realized i recognized 1 of the screen names as some 1 from my other screen name but this persondoesn'tt know the screen name i was on and just like the rest she just buzzed me butdidn'tt say anything.whats going on?