Hawking made -again- a fundamental error in his "We should not broadcast to aliens that we are here" piece. As Seth Shostak points out, we have been doing so for 70 years, but even that is an error of sorts.
Radio waves and signals began in the 1920s and are now MANY light years out in space. Radio/radar testing and broadcasts as well as nuclear tests from the 1940s prior to 1944 will be "out there"
Far, far older civilisations than ours would have had their own SETI and spotted our Earth. However, the question is would WE go to a planet that has never seen peace? Destroys its environment at an alarming pace? If they are watching our TV broadcasts and listening to our radio it is far more likely Earth and Humans would be on a Quarantine list.
REAL science would combine SETI with investigation of high graded reports of "UFO" landings because if just one out of 1000 such reports -even 5000- was real......
It's a brief video so why not watch it?