I think it's a Wardialer looking for businesses to hack into...When the wardialer app dials a phone number it looks for a modem; not a human. When someone answers a number, it hangs up and makes a note of it for the hacker to ignore. That's my guess.
It's one of those calls that pretend to be the IRS threatening you to give them money. It's a complete scam, and they've called me three times since yesterday.
Received a call. As the others, no response. Called back, robot said I couldn't do anything. I'm incensed. I don't even know who called me. I don't know why. I'm on a registered 'no call' list.