Cookie syncing

Cookie syncing, cookie synchronization or cookie matching is a technique in online advertising to track users across multiple websites. Once users see an advertisement, user data in the form of cookies is shared among ad companies, allowing them to link identifiers and create a user-specific profile to optimize targeted advertising. The process increases the relevance of personalized ads shown to the user, but raises privacy concerns in the way it enables companies to track people across the internet without their direct knowledge or explicit consent. Cookie syncing can also expose personal information, weaken security, and is difficult for users to avoid, even if they attempt to delete cookies on their device. The practice is widespread among major advertising networks. In Europe, the General Data Protection Regulation led to a decrease in cookie syncing compared to the United States.