The Shadowserver Foundation confirmed the 100 figure. It said most of those affected were in the United States and Germany, and the victims included government organizations. Another researcher said that, so far, the spying appeared to be the work of a single hacker or set of hackers.

Hackers have used a zero-day exploit in SharePoint to carry out attacks on businesses and at least some U.S. government agencies.

Microsoft issued an alert on Saturday that said the server software being targeted is used by government agencies and businesses to share documents within their organizations.