To Wait For the Signal
In 1977 the Big Ear-observatory received a signal which some considers the most conspicous evidence so far for the existence of extraterrestrial civilisations. It was possible to exclude most natural and Earth-based explanations of the signal's origin. Unfortunately, the signal was never repeated. Any potential details of artificial information was not possible to obtain, since the technology of 1973 did not allow such close scrutiny of the signal. In spite of several follow-up observations with much more powerful and modern equipment, no further clues have ever been found.
Nevertheless, the search for similar signals is continuing. The perhaps most promising radio observatory of today, the Allen Telescope Array, is primarily dedicated for SETI investigations.
SETI alive and kicking?
A major initiative to intensify SETI research is under way. Russian billionaire Yuri Milner spends $100 million during ten years to support monitoring a million of the stars closest to Earth, as well as the hundred nearest galaxies. Two of the world's largest radio telescopes, at the Parkes and Green Bank observatories, will be used.