Third-party processing is when a service sends user data to an outside vendor that handles it on the service’s behalf. Common examples include cloud hosting, analytics, customer support platforms, payment processors, and advertising partners. The service may still control the purpose of processing, but the vendor can store, copy, enrich, or transmit the data within agreed limits.
It matters because every extra processor increases the attack surface and the privacy risk. If a vendor is compromised, misconfigured, or given overly broad access, sensitive data can leak without the core application being directly hacked. Defenders reduce this risk with data minimization, strict contracts, access controls, encryption, vendor reviews, and logging of data flows. In real incidents, attackers often target weaker third parties or abuse legitimate integrations to move data beyond the original service’s control.