The virus is a classic proof-of-concept, written to show that it's possible to create a cross-platform virus, Kaspersky said. "However, our experience shows that once proof-of-concept code is released, virus writers are usually quick to take the code and adapt it for their own use," Kaspersky said.

That concern is shared by Swa Frantzen, who tracks incidents at the SANS Internet Storm Center, which monitors network threats. "The impact of the proof-of-concept at this point is very low in itself, but it is a sign the cross-platform aspects are becoming important," Frantzen wrote on the ISC blog. "As the developers of viruses continue to research this, we will see more cross-platform malware come about in the future."

Kaspersky has added detection for the malicious software to its antivirus databases.

The researchers altered the genes of a laboratory strain of a virus called M13 so that its outer layer would bind metal ions.

They grew the viruses inside bacteria in a solution of cobalt chloride so that crystals of cobalt oxide would collect on the viruses.

The international team of researchers, led by Massachusetts Institute of Technology professors Angela Belcher, Paula Hammond and Yet-Ming Chiang, also added gold to the mix so that batteries built using this technique will be able to carry more charge.

The viruses were placed between two oppositely charged plates and, because the viruses are negatively charged, they collected into uniform, flexible sheets.

The film of metal-coated viruses can serve as an anode, a positively charged electrode in a battery.

The chemical reactions involved in building the nanowires took place at normal room temperature and pressure, and didn't need expensive pressure-cooking techniques to complete, the researchers said.

Each virus essentially becomes a nanowire 880 nanometres (880 billionths of a metre) long and six nanometres in diameter, the same dimensions as the virus.

The document also shows the location where a terrorist armed with a high-caliber sniper rifle could detonate the tanks that supply oxygen to Air Force One's medical facility.

As of Friday, the document was still posted online. The Secret Service refused to comment on the document's release.

"It is not a good thing" for that information to be in the public domain, said Lt. Col Bruce Alexander, director of public affairs for the Air Mobility Command's 89th Airlift Wing, Andrews Air Force Base, which operates the presidential air transport fleet. "We are concerned with how it got there and how we can get it out. This affects operational security."

Information about Air Force One's anti-missile systems is considered particularly sensitive.

"Having information about a target's countermeasures does two things," said Daniel Goure of the Lexington Institute. "It gives you an opportunity to choose a different weapon and to choose a different attack style ... perhaps choosing to launch a salvo attack, or choose a missile that uses an active beam."

"It is tough enough for the Secret Service to do its job without this," said Leon Panetta, former chief of staff to President Bill Clinton, who now runs a public policy study center at California State University at Monterey Bay. "If I were still chief of staff, I would order the damned site (to) pull it down."

"This is a significant stage in the development of our cooperation, and the fact that the turbine was up and running at the first attempt is an unprecedented case in the construction of Russian nuclear power plants," said Kiriyenko, who is visiting the Indian city of Mumbai as part of an Asian tour.

The turbine will be linked into China's electricity grid by the end of April and come online in fall, the Nuclear Power Agency said.

State nuclear technology export company Atomstroiexport has been helping China build the Tianwang facility in eastern Jiangsu Province under a 1997 contract signed following an intergovernmental agreement.

"This is a new step by Russia in conquering the international nuclear machinery market," a company spokesman said.

The Tianwang project will use VVEP-1000/428 pressurized water nuclear reactors with improved safety systems and neutron properties.

Smaller particles reflect blue light, giving the ring its distinctive colour, the US team reports in Science.

All other rings - those around Jupiter, Saturn, Uranus and Neptune - are made up of both large and small particles, making the rings reddish in appearance.

Bright blue

Astronomers have long known that the gas giant Uranus is surrounded by rings of dark particulate matter up to ten metres in diameter.

But last December, two new rings - the planet's twelfth and thirteenth - were discovered using the Hubble Space Telescope.

Astronomers observed the ring system at infrared wavelengths with the Keck telescope, in Hawaii.

The outermost ring, and its ice-bound moon Mab, could not be observed in infrared light unlike the red inner ring.

A team led by Imke de Pater, professor of astronomy at the University of California, Berkeley, found that the ring was bright blue, something of an oddity in planetary terms.

"The blue colour says that this ring is predominantly submicron-sized material, much smaller than the material in most other rings, which appear red," Professor de Pater said.

The tiny particles - less than a thousandth of the width of a human hair - scatter and reflect predominantly blue light, much like the very small molecules in the air that make the Earth's sky blue.

The more common rings are reddish because they also contain many larger particles, which gives the reflected light its colour, and may be made up of reddish material, perhaps from iron.

It appears that the outer blue rings of Saturn and Uranus are strikingly similar, not least because they are both associated with small moons.

Moon dance

"The moon orbits the planet in the ring," Professor de Pater told the BBC News website.

"It is continuously impacted by very tiny particles [micrometeorites]. On a moon that doesn't have any atmosphere these tiny particles impact the moon at high velocity, and throw stuff up into space.

"Because the moon is so small, it escapes the moon and goes into orbit around the planet.

"The smaller particles stay in orbit around the planet but the larger particles smash back into the moon."

The work was carried out in collaboration with Mark Showalter, of the Search for Extra-Terrestrial Intelligence (Seti) Institute in California; Heidi Hammel, of the Space Science Institute, Colorado; and Seran Gibbard, of Lawrence Livermore National Laboratory in California.

The scientists plan to carry out further observations next year, when the faint rings of Uranus will be more visible.