Platforms such as WhatsApp, Signal, and Telegram are increasingly popular destinations for group messaging worldwide because they offer guaranteed privacy: messages are encrypted so that the platforms themselves cannot read them. While this privacy offers many benefits, it also means that platforms can’t see or moderate disinformation. Links to disinformation can spread rapidly through these popular platforms through family and friend groups without any opportunity for the platform to intervene. The team will create and launch Lighthouse, an application for Android mobile phones that privately notifies users of disinformation links they receive through the WhatsApp end-to-end encrypted messaging platform. Because WhatsApp cannot itself identify disinformation links in messages, Lighthouse will identify these links locally on the user’s phone and will then notify the user if they have received a link to a known disinformation URL.