Google stepped up its effort Wednesday to make it tougher for spies or anyone else to snoop on email, unveiling Chrome browser software for scrambling digital messages.

A test version of a software tool called "End-to-End" was released so Internet engineers can dabble with making mini-programs that plug into Chrome browser and encrypt Gmail messages in ways that shield them from eyes of everyone except senders and recipients.

"Emails that are encrypted as they're routed from sender to receiver are liked sealed envelopes, and less vulnerable to snooping -- whether by bad actors or through government surveillance -- than postcards," Gmail delivery team tech lead Brandon Long said in a blog post.

Along with releasing the encryption tool, Google added a section to its Transparency Report showing what portion of Gmail messages were sent wrapped in encryption and similar information for digital missives received from other email services.

The report showed on Thursday that over the past month 69 percent of outgoing Gmail messages were encrypted while only 48 percent of the email received from other services was scrambled in transit.

In a move that promised to pressure other services, Google broke down how much message traffic received from them was encrypted.

US Internet service titan Comcast, which got a dismal ranking in the report, quickly stepped up to say it is ramping up message encryption.

"Many providers have turned on encryption, and others have said they're going to, which is great news," Long said.

"As they do, more and more email will be shielded from snooping."

The move by California-based Google comes as US Internet firms fend off privacy concerns provoked by US online spying tactics exposed by former intelligence agency contractor Edward Snowden, who has taken refuge in Russia.

gc/rl