The Appsero analytics tool, which is used in many plugins, was found to have a security vulnerability. This means that someone without proper permission could change the data without authorization. The issue was specifically with the handle_optin_optout function in versions up to and including 2.0.0. This allowed attackers who were not authenticated to either opt-in or opt-out of tracking. The problem was fixed in version 2.0.1 of Appsero by adding a nonce check.