In one aspect, a system includes a transaction handler to process transactions, a data warehouse to store transaction data recording the transactions processed at the transaction handler and to store mapping data between first user identifiers and first account identifiers, a profile generator to generate a profile of a user based on the transaction data, and a portal coupled to the transaction handler to receive a query identifying a second user identifier used by the first tracker to track online activities of a user. The system is to identify a second account identifier of the user from the second user identifier based on the mapping data between the first user identifiers and the first account identifiers to facilitate targeted advertising using the profile of the user and/or to provide information about certain transactions of the user related to a previously presented advertisement.