A search for intelligent life in space has drawn a blank.
Scientists have found no signs of alien beings after analysing radio signals collected in the world's biggest distributed computing project.
More than 150 candidates selected by the Seti@home project have been examined using the giant Arecibo radio telescope in Puerto Rico.
Astronomers say they have discovered no evidence of a signal from an extraterrestrial civilisation during a quick, real-time analysis of the data.
However, they intend to take a more thorough look at the results over the next few weeks, with the help of Seti@home volunteers.
Susan Lendroth, of the Planetary Society in Pasadena, California, US, which sponsors Seti@home, said they had not expected a quick result.
She told BBC News Online: "The odds are probably against a quick find but Seti researchers around the world hope that they will one day find evidence of an alien civilisation."
People power
Since 1999, millions of people from more than 200 countries have been running a special screensaver program on their desktops.
It uses idle time on a PC to sift data obtained by radio telescopes for patterns that might represent a communication from space.
The observations in Puerto Rico took place over three days. Data was collected on 166 promising radio signals, exceeding the original goal of 150.
Other sources were observed, including extra-solar planetary systems (that might contain Earth-like planets), nearby galaxies and Sun-like stars.
Bruce Betts of the Planetary Society said the unique aspect of the project was that the public participates in real scientific analysis.
"Millions of people around the world have helped get us to the point where we could identify potential targets and take a second look," he said.
"Now the new data will go back to the Seti@home volunteers for more help with this early but critical step in our continuing search for extraterrestrial intelligence."
Seti@home, which is based at the University of California, Berkeley, was founded by the Planetary Society four years ago.
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