1. A computer-implemented method for providing personalized advertisements to a user, the method comprising selecting a plurality of advertisements for display to a user of a computer system, the advertisements selected according to an estimated probability that the advertisements are of interest to the user, wherein selecting the advertisements comprises: monitoring user interactions with content while the user is engaged in use of a computer; analyzing the monitored interactions to estimate parameters of a user specific learning machine; identifying properties of candidate advertisements; applying identified properties of the candidate advertisements to the user specific learning machine to estimate a probability that one or more of the candidate advertisements are of interest to the user; providing, from a server to the computer, one or more of the candidate advertisements as the selected advertisements; and presenting, via a browser running on said computer, the one or more selected advertisements in conjunction with a first web page.