WhatsApp, the globally popular instant messaging system owned by Facebook, has begun using a powerful new encryption program aimed at protecting users' conversations from unwanted surveillance and snooping.

The messaging service, which has 600 million users and is especially popular in Europe and Asia, added the new encryption to its last update for Android smartphones, according to Open Whisper Systems, the San Francisco-based software group that developed the "TextSecure" program with help from U.S. government grants and private funding.

Privacy advocates say WhatsApp's decision to incorporate so-called "end-to-end" encryption will help users communicate without the fear of someone reading their messages. WhatsApp cofounder Jan Koum has said he's deeply committed to user privacy because he grew up in the Soviet Union during the 1980s, when his mother and other adults routinely assumed that authorities eavesdropped on their phone calls. The move comes as other leading tech companies also are boosting data encryption, despite criticism from some in law enforcement who say that can make it more difficult for authorities to catch terrorists or other criminals.

Google Inc. and Facebook Inc. encrypt users' email and messages while they move within each company's network, so they can't be read by outsiders. But experts say those messages can still be scanned at certain points by the companies themselves, for commercial purposes such as advertising, and can be read by authorities if subpoenaed. Apple and Google also encrypt user data when it's stored on their mobile devices.

TextSecure takes that a step further; it's designed to make WhatsApp messages unable to be read by anyone but the sender and recipient, even if subpoenaed. The encryption feature is offered by default, meaning WhatsApp users don't have to turn it on and shouldn't notice its presence, according to a statement from Open Whisper Systems. WhatsApp declined comment Tuesday.

Apple's iMessage service also encrypts data from "end-to-end" but some experts say Apple's program has technical features that may leave it vulnerable to determined snooping. TextSecure isn't yet available for WhatsApp on iPhones, but Open Whisper said it is working to make the feature available to iOS and other non-Android mobile users.