Invite links for WhatsApp and Telegram groups that may not be intended for public access are available through simple lookups on popular web search engines.
Both companies took some steps to protect the privacy of their users but more effort is necessary to make the links completely non-discoverable via public searches, thus allowing anyone to find them and join the group.
The issue was signaled on Friday by Jordan Wildon, multimedia journalist at Deutsche Welle, who warned that the lapse allowed the discovery of some unexpected, even groups for illegal activities.
Jane Wong, a mobile app reverse said that her Google search revealed around 470,000 results for WhatsApp invite links, allowing anyone to join the groups and access to members' phone numbers.
In all fairness, the privacy of these links is the responsibility of the admins generating them. By sharing them on the surface web - the internet that is indexed by conventional search engines - is a sure way to have them indexed by public search services.
Google's public search liaison Danny Sullivan explained that this is normal behavior, the same as when "a site allows URLs to be publicly listed."
Using special search parameters, several users discovered that Telegram channels were in the same situation. It is unclear whether the admins made the invite links discoverable knowingly or in error. Regardless, some very unsavory results are not difficult to find.