Purchase Details Leaked to PayPal

We describe a new form of online tracking: explicit, yet unnecessary leakage of personal information and detailed shopping habits from online merchants to payment providers. In contrast to Web tracking, online shops make it impossible for their customers to avoid this proliferation of their data. We record and analyse leakage patterns for N = 881 US Web shops sampled from Web users' actual online purchase sessions. More than half of the sites shared product names and details with PayPal, allowing the payment provider to build up comprehensive consumption profiles across the sites consumers buy from, subscribe to, or donate to. In addition, PayPal forwards customers' shopping details to Omniture, a third-party data aggregator with an even larger tracking reach. Leakage to PayPal is commonplace across product categories and includes details of medication or sex toys. We provide recommendations for merchants.