Microsoft’s move to expand encryption would allow it to join Google , Yahoo , Facebook and other major technology firms in hardening its defenses in response to news reports about once-secret NSA programs. The resulting new investments in encryption technology stand to complicate surveillance efforts — by governments, private companies and criminals — for years, experts say.

Though several legislative efforts are underway to curb the NSA’s surveillance powers, the wholesale move by private companies to expand the use of encryption technology may prove to be the most tangible outcome of months of revelations based on documents that Snowden provided to The Post and Britain’s Guardian newspaper. In another major shift, the companies also are explicitly building defenses against U.S. government surveillance programs in addition to combating hackers, criminals or foreign intelligence services.

“That’s a pretty big change in the way these companies have operated,” said Matthew Green, a Johns Hopkins University cryptography expert. “And it’s a big engineering effort.”

In response to questions about Microsoft, the NSA said in a statement Tuesday, “NSA’s focus is on targeting the communications of valid foreign intelligence targets, not on collecting and exploiting a class of communications or services that would sweep up communications that are not of bona fide foreign intelligence interest to the U.S. government.”