According to Rajshekhar Rajaharia, the web version of the messenger has a loophole that causes these numbers to be indexed by Google. This problem happens mainly when the user activates web mirroring of the application:
The leak is happening via WhatsApp Web. If someone is using WhatsApp on a laptop or office PC, their mobile number will be indexed in Google Search. We are talking about individual user numbers, not business phones.
The messenger has previously been alerted to the privacy breach. The solution found was to ask Google not to index the numbers and links. However, everything still needs to be improved.
For now, Google has yet to comment on the Indian researcher’s discovery. WhatsApp says that it has already solved the problem involving the indexing of numbers and links through the address “website: chat.whatsapp.com”.
In addition, a spokesman for the messenger clarified that since March 2020 the links have the tag “noindex” to prevent the problem from recurring. However, the company said nothing about the new security hole in WhatsApp Web.