1. One or more non-transitory computer-readable storage mediums storing one or more sequences of instructions for executing a virtualized web browser, which when executed by one or more processors, cause: upon the virtualized web browser being instructed to display a web page having one or more portions of data, the virtualized web browser consulting a set of policies, defined in policy data, to dynamically identify from among one or more virtual machines, which virtual machines should be assigned the responsibility of retrieving and rendering the one or more portions of said web page, wherein said set of policies further identifies and assigns a different virtual machine in said one or more virtual machines for each portion of the web page that is associated with an iFrame, such that each of said different virtual machine retrieves and renders all content for its corresponding iFrame; the virtualized web browser instructing said identified one or more virtual machines to retrieve content for at least a portion of the web page; each of the one or more identified virtual machines (a) retrieving across a network a set of content whose retrieval was delegated to that identified virtual machine, and (b) rendering said set of content retrieved by that identified virtual machine, by generating a graphical representation from the retrieved content; and upon the virtualized web browser obtaining the rendered screen data content from the one or more virtual machines, the virtualized web browser displaying the web page using the obtained rendered screen data content.