How do you work out if a signal from space is a message from aliens?

Astronomers working at the Arecibo radio telescope in Puerto Rico havedetected a weird radio signal, spotted when pointing their telescope at the nearby star Ross 128. They’re not getting too excited about the prospect of an alien civilisation contacting us just yet though. “In case you are wondering, the recurrent aliens hypothesis is at the bottom of many other better explanations,” said Abel Mendez, the scientist leading the campaign.