Abstract: An online advertising system includes a computer system that receives conversion data and other event-level data from an ad server computer or a computer of another third party collecting data from or associated with an ad as well as non-personally-identifiable customer data from an advertiser. The computer system uses a customer ID or order ID as a common link to correlate customer data of an advertiser associated with such customer ID or order ID with one or more unique identifiers associated with a particular browser and the online behavior and advertising metrics associated with such unique browser identifiers. The computer system is therefore able be used by advertisers to measure the effectiveness of their online advertising activities and deliver precisely targeted ads to users without tracking the online behavior of their customers, whose online behavior is rendered anonymous.