T-Online.de

T-Online experienced a significant data security incident involving the exposure of user credentials. The breach originated from a third party service provider that managed promotional activities for the German telecommunications giant. The leaked data contained authentication details and personal identifiers of millions of customers. Security researchers identified that the information was circulating in underground forums and being used for credential stuffing attacks against other platforms. The incident highlighted vulnerabilities in supply chain security and the risks associated with sharing customer data with external marketing partners.