The SETI@Home project, that has seen over five million computer users donate run time to the search for extra terrestrial life, is facing closure because of a lack of cash.

The project needs to raise £750,000 by the end of the year and writer and futurologist Sir Arthur C Clarke has sent out a letter urging computer users to send in donations. The project is updating its hardware and software and is running dangerously low on funds. 

"Following the "dot com" bust, the commercial support that kept SETI@home running has largely disappeared," he writes.

"Because of this loss of support, we can no longer count on matching funds from the University of California. We are rapidly approaching the end of what funds we do have."

The team have set up a special site where donors can contribute to the project.

The SETI@Home prioject was launched in 1999 and was the first large scale software that used the spare capacity of ordinary PCs to process data that would usually be done by supercomputers.

The data comes from the Arecibo Observatory and so far over 2.4 million years of processing time have been used to search for extraterrestrial intelligence.