Bing joins Google and Yahoo, which have been making encryption standard as part of an effort to thwart snooping, amid heightened concerns since the leak of documents in 2013 by former US intelligence contractor Edward Snowden.

"Microsoft has a long history and deep commitment to helping protect our customers' data and the security of their systems," Forrester said.

"While this change may impact marketers and webmasters, we believe that providing a more secure search experience for our users is important," he said.