WhatsApp does not break end-to-end encryption for messages that are reviewed by the 1,000-strong contract workforce it employs to review content flagged by users.

       A ProPublica piece on Tuesday raised questions about WhatsApp not being transparent about reading people's messages, and detailed how content reviewers look at flagged content for "claims of everything from fraud or spam to child porn and potential terrorist plotting".

       A clarification to the story, published by the news site on Wednesday said, "A previous version of this story caused unintended confusion about the extent to which WhatsApp examines its users’ messages and whether it breaks the encryption that keeps the exchanges secret. We’ve altered language in the story to make clear that the company examines only messages from threads that have been reported by users as possibly abusive. It does not break end-to-end encryption."

       WhatsApp has detailed how it looks and reviews content in a whitepaper in February 2019.

       "Given the nature of end-to-end encryption, we focus on the behavior of accounts and user-reported content. We employ a team of engineers, data scientists, analysts, and researchers with a wide range of backgrounds and expertise to deter and prevent abuse," the whitepaer explains.

       The Facebook-owned messaging service also said at the time that it scans unencrypted information like profile photos for child exploitative imagery.

       Much of the reporting made to WhatsApp goes into training its machine learning algorithm.

       "Machine learning models require basic components known as features, labels, and infrastructure to complete their tasks. Features are the specific signals — such as number of reports, rate of messaging, reputation of other users sharing the same computer network, and so on—that provide insight into abusive behavior. We use labels to mark the worst offenders and distinguish between their behaviours from those of regular users," it said in the same whitepaper.

       Updating some parts of its published article, ProPublica said Wednesday: "The workers have access to only a subset of WhatsApp messages — those flagged by users and automatically forwarded to the company as possibly abusive. The review is one element in a broader monitoring operation in which the company also reviews material that is not encrypted, including data about the sender and their account."