1. In a computer network having one or more servers connectable to one or more clients, a method of monitoring user interaction with a file downloaded from a server, comprising the steps of: using a client to specify an address of a resource located on a first server; downloading a file corresponding to the resource from the first server in response to specification of the address; using the client to measure the amount of time the user spends interacting with or displaying the file downloaded from the first server; using a server to acquire client identifying indicia from the client; and uploading the amount of time measured by the client to a server.