SHGb02+14a, the SETI@home signal
The account
A signal from an empty patch of sky, near the hydrogen frequency, was thought to be a call from another civilization.
What investigators found
The SETI@home team itself considers it more likely to have been noise or a statistical fluke.
The story
SETI@home turned millions of home computers into one vast analysis network. Volunteers around the world let a screensaver crunch data from the Arecibo radio telescope in search of artificial signals. Among the candidates that drew the most attention was SHGb02+14a, reobserved in 2003 in a region between the constellations Pisces and Aries where there is no visible star nearby.
The detail that fired imaginations was the frequency, close to the natural emission of hydrogen, a band many researchers considered a logical choice for anyone who wanted to be heard. But the signal was weak and drifted in frequency far too quickly, something hard to explain even for a transmitter on a rotating planet. The project's leaders said it was most likely equipment noise or statistical chance. It was never detected again.