1. A method on a peer client for assisting in delivering update contents in a computer network, the method comprising: communicatively coupling a first peer client to at least one other peer client on a computer network including a server; receiving at the first peer client at least one update notifications from the server, the at least one update notification having been received by the server from the at least one other peer client; identifying, with at least one computer processor, friends involved an interaction history of a user of the first peer client with the server; calculating, with at least one computer processor, a concern degree d m =C m,n /a m of the user n for each friend m, where C m,n is number of interactions between the friend m and the user n, and where a m is number of update notifications made by the friend m; creating, with at least one computer processor, a friend list consisting of friends that have a concern degree higher than a threshold; evaluating with at least one computer processor, a user's an interaction preferance of the user according to a user's interaction history utilizing at least the friend list, wherein the friend list is created by considering a hit ratio h n as follows h n ⁢ ∑ m = 0 M n - 1 ⁢ p m , n · s m , n = ∑ m = 0 M n - 1 ⁢ c m , n ∑ m = 0 M n - 1 ⁢ c m , n · s m , n , where P m,n is C m,n divided by number of interactions of user n with all users and where S m,n =1 when user m is added to the friend list and S m,n =0 when user m is not added to the friend list; in response to an update notification received fromt the server, determining whether to prefetch update contents corresponding to the update notification according to the interaction preference; and in response to evaluating to prefetch, obtaining the update contents directly from the at least one other peer client in a peer-to-peer manner and storing the update contents locally on the first peer client.