A for Andromeda (Rare, 1962)

A new radio telescope picks up from the constellation of Andromeda a complex series of signals which prove to be a programme for a giant computer. After the computer is built it begins to relay information from Andromeda. Scientists find themselves possessing knowledge previously unknown to mankind, knowledge that could threaten the security of human life itself.

From the back cover:

“The faint crackling noises from the loudspeaker in the control room of the big observatory were definitely signals. Someone ..or something… far out in space was trying to make contact.
Young Dr. Fleming and his colleagues were not superstitious. They were scientists. But none of them could deny the chill of fear that suddenly swept over them.
Still there was nothing really to warn them of the danger the hideous nightmare that was about to envelop them all.
They had no way of knowing that a monstrous intel-ligence from outer space had already reached into their minds… that they were already victims helpless conspirators in a silent, invisible conquest of earth. “