8. The computer-readable storage medium of claim 6 , wherein analyzing content download descriptions comprises: analyzing a content download description for an executable content download using a trusted user-agent string to determine an identifier of a network location from which the content was downloaded; and adding the identifier of the network location to the white list of legitimate content.
9. The computer-readable storage medium of claim 8 , wherein the client is further adapted to determine that executable content downloaded from the network location identified by the identifier added to the white list is legitimate.