HelpNetSecurity has disclosed that up until recently it was possible to send a innocent image containing malicious code to WhatsApp and Telegram clients. Once clicked, the attacker would gain complete access to their accounts, accessing all conversations, photos, videos, etc. The root of the issue seemed to be that since the messages were end-to-end encrypted, WhatsApp and Telegram couldn't filter transmissions for malicious content. The Whatsapp and Telegram teams apparently did a good job at responding quickly to this vulnerability and patching it up.