A Russian cosmonaut claims to have found "alien life" on the International Space Station, but even if true the discovery is sadly far less exciting than Hollywood films would have us believe.

It turns out our first contact with extra-terrestrial life wasn't a grey alien with black eyes, but rather it was more a microscopic scale discovery, Anton Shkaplerov reportedly says.

While conducting space walks outside the International Space Station, he discovered tiny bacteria that doesn't come from Earth, Shkaplerov told Russian state media.

"Now we have found bacteria that lived there for three years in a space environment, where the vacuum and temperature range from minus 150 to plus 150, and remained alive," he told Tacc.

Shkaplerov said the Russian space agency frequently takes cotton swabs from the outside of the station in predetermined locations and this is how the discovery was made.

"It turned out that from somewhere on these swabs bacteria were found that were not present when the ISS module was launched," he said.

"That is, they came from somewhere from outer space and settled on the outside of the skin. While they are being studied and, it seems, there is no danger."

Although the idea of alien life is exciting, the cosmonauts can't rule out that the bacteria have earthly origins.

As bacteria can live in extreme conditions like those in space, it's possible - in fact many argue probable - that the undiscovered microbes living in earth's upper atmosphere could have been picked up on the space station since the launch.

The bacteria has been brought back to earth on the swabs to be further studied.