A number of Greenpeace activists climbed the 20 meter glass wall outside of the Microsoft building in Herzliya Tuesday morning and even cleaned the building's windows for more than an hour to protest the fact that the computer giant still uses coal to power its data centers. Police officers who were dispatched to the scene ordered the activists to clear the area. The stunt was part of the environmental group's global campaign calling on Microsoft to use more environmentally-friendly energy resources. Banner on Microsoft building (Photo: Dor Nevo) The activists opened a 100 square meter banner from the building's roof which read “still using coal” and "clean up your cloud from coal." The messages are a reference to Microsoft's data centers, known as the "cloud." The act of cleaning was symbolic of Greenpeace's demand that Microsoft use "cleaner" energy resources. A recent report published by Greenpeace called out Microsoft, Apple and Amazon as having some of the dirtiest "clouds" in the industry. The report said these companies are “rapidly expanding without adequate regard to (the) source of electricity and rely heavily on dirty energy to power their clouds." Yahoo, Google and Facebook, on the other hand, were praised for using renewable energy. Greenpeace activist Hila Krupsky said Tuesday's stunt was aimed at sending Microsoft a clear message: "As customers who use Microsoft's new technologies on a daily basis, we expect the company to stop sustaining the technology of the future with dangerous, polluting and obsolete energy from the 19th century." Microsoft said in response that it is "committed to preserving the environment and is making every effort to reduce energy consumption in all its businesses. The past three years have seen a 50% drop in energy consumption at the company's new server farms." Reuters contributed to the report Follow Ynetnews on Facebook and Twitter