Activists rappelled down a Seattle office building Thursday to get Microsoft and Amazon.com to use clean energy to power datacenters running services based in the Internet "cloud."

Two Greenpeace members launched from the roof of a new headquarters being built for Amazon.com, across a street from Microsoft offices, to hang a cloud-shaped banner with a message asking the companies "How clean is you cloud?"

"People want to use innovative devices and technology like the Kindle and Windows Phone without having to connect to a cloud powered by dirty and dangerous energy," said Greenpeace International analyst Casey Harrell.

"Amazon and Microsoft have the potential to power their cloud with green, renewable energy, but are falling behind competitors Google, Facebook and Yahoo! in the race to build a truly clean cloud."

The stunt came on the heels of a Greenpeace report grading major technology firms on the use of renewable energy sources to meeting rocketing datacenter demands and marked the start of a Clean Our Cloud campaign.

Amazon, Apple and Twitter were graded poorly in a Greenpeace study of technology titans' use of clean energy to power the mushrooming Internet cloud, but Facebook, Google and Yahoo! won praise.

The environmental charity's report, billed as a rallying cry instead of a critique, related to the companies' use of data centers and other energy issues.

Both Amazon and Microsoft datacenters rely heavily on "dirty and dangerous coal and nuclear power," according to the report.

Greenpeace called on all technology firms using datacenters to provide online software or services to be more open about energy use and to shift to non-polluting sources of power.

Amazon.com said information about it in the Greenpeace report was "inaccurate."