Obviously, they're not within 70 light years away, the amount of time that earthlings have started broadcasting radio waves to the rest of the universe. Even if there were ETs within that distance, it would take them another 70 years to answer back to us So, it would be better for astronomers here on earth to listen for radio waves or other signals from ETs and answer them then they're detected..
More likely, the ETs would be living more than 70 light years away from earth. If we did hear signals from these ETs, they would more likely have the same level of technology than us. They're more likely not able to travel to earth any time soon. So, they're more likely a type 0 civilization, a civilization less than the Star Trek TV series shown in the in the mid-1960s. So, Steven Hawking's fear of advanced ETs, who may attack the earth because of our radio signals, would be groundless.
