Google has enhanced the encryption technology for its flagship email service in ways that will make it harder for the National Security Agency to intercept messages moving among the company’s worldwide data centers.

Among the most extraordinary disclosures in documents leaked by former NSA systems analyst Edward Snowden were reports that the NSA had secretly tapped into the main communications links that connect Yahoo and Google data centers around the world.

Google, whose executive chairman, Eric Schmidt, said in November that he was outraged over the practice, didn’t mention the NSA in Thursday’s announcement, except in a veiled reference to “last summer’s revelations.”

Yahoo has promised similar steps for its email service by this spring.

Google and other technology companies have been outspoken about the U.S. government’s spy programs. The companies are worried more people will reduce their online activities if they believe almost everything they do is being monitored by the government. A decline in Internet use could hurt the companies financially by giving them fewer opportunities to show online ads and sell other services.

“Your email is important to you, and making sure it stays safe and always available is important to us,” Nicolas Lidzborski, Gmail’s security engineering lead, wrote in a blog post.

Lidzborski said that all Gmail messages a consumer sends or receives are now encrypted.

“This ensures that your messages are safe not only when they move between you and Gmail’s servers, but also as they move between Google’s data centers — something we made a top priority after last summer’s revelations,” Lidzborski wrote.

A secret Jan. 9, 2013, accounting indicated that NSA sends millions of records every day from Yahoo and Google internal networks to data warehouses at the NSA’s Fort Meade, Md., headquarters, according to documents released by Snowden and obtained by The Washington Post last year.

The NSA’s principal tool to exploit the Google and Yahoo data links is a project called MUSCULAR, operated jointly with the agency’s British counterpart, GCHQ. NSA and GCHQ are copying entire data flows across fiber-optic cables that carry information between the data centers of the Silicon Valley giants, the Post reported.

The NSA has said it only focuses on targets with foreign intelligence value.

(AP)