Received a call, I picked up but didn't speak. (Alas, there was background noise which I was trying to prevent from happening). After the now-identified 3 second pause, the robo caller hung up. I'm sure it was a robo call. Certainly a spam / silent call that is searching for a legitimate phone number (mine) to send further phishing calls to (by listening to background noise and voices). I've had thousands of these calls now and I currently receive, by far, more phishing, spam, hoax & threatening calls by criminals than I get from businesses, health care workers and people I know, combined.