To reinforce the real-world value of contact secrecy, let me share an example of how WhatsApp's contact broadcasting is creating massive opportunities for scamm

To reinforce the real-world value of contact secrecy, let me share an example of how WhatsApp's contact broadcasting is creating massive opportunities for scammers where I live (Mexico). In WhatsApp, when you join a "community" (sort of like a giant, moderated group), all members of the community are visible to all other members. You can see their phone numbers and their self-chosen nickname. Note that very frequently people will have their names or a shortened version of their name as their nickname. In emerging markets, people use WhatsApp for everything and many people will naturally join a few communities. Things like: - A community for your kid's school - A community for your neighborhood's safety alerts. - A community for a club or hobby. So a scammer's workflow is as follows: 1. Infiltrate a community or a group. 2. Check all of the members and find those whose names are publicly shared or you can deduce. 3. Use their name, phone and--crucially--information about the community itself to craft a targeted phishing phone call. Example: Sandra is a part of a community for neighborhood safety news. The community is called "Hillsborough safety." Her whatsapp nickname is "Sandy Williams." A scammer will join the community and see her contact. They will then call her with a message like "Hi, is this Sandra Williams? Yes, I'm calling from the Hillsborough police department. Unfortunately there's been an accident with your husband...". You can imagine how the simple fact of knowing someoen's name and some sort of "proprietary knowledge" (they know I live at Hillside!) can be enought to for a victim to lower their defenses. An additional layer to this is that often the scammer will social-engineer their way into gaining access to the victim's Whatsapp account itself. They can then access all of the groups that victim was a member of, including "tight" friend groups, etc. IMHO contact broadcasting is an inexcusable design decision by WhatsApp.