A group of crytopgraphers from Germany's Ruhr University Bochum have uncovered flaws in WhatsApp's security that compromise the instant messaging service's end-to-end encryption. WhatsApp, owned by Facebook, has over one billion active users. In a paper published last week, "More is Less: On the End-to-End Security of Group Chats in Signal, WhatsApp, and Threema," anyone who controls WhatsApp's servers, including company employees, can covertly add members to any group -- a claim that might not bode well with privacy enthusiasts. From the paper: The described weaknesses enable attacker A, who controls the WhatsApp server or can break the transport layer security, to take full control over a group. Entering the group however leaves traces since this operation is listed in the graphical user interface. The WhatsApp server can therefore use the fact that it can stealthily reorder and drop messages in the group. Thereby it can cache sent messages to the group, read their content first and decide in which order they are delivered to the members. Additionally the WhatsApp server can forward these messages to the members individually such that a subtly chosen combination of messages can help it to cover the traces. Further reading: Wired.