6. A computer-readable storage medium containing instructions for controlling a computing device to rank web pages, by a method comprising: providing a first web graph representing links between the web pages at a first time and a second web graph representing links between the web pages at a second time that is later than the first time; determining a first ranking of the web pages based on the first web graph by: initializing a first jumping vector to indicate probabilities of visiting the web pages without using a link, the initializing including setting the probability of visiting a suspected spam web page without using a link based on confidence that the suspected spam web page is actually spam so that the set probability decreases as the confidence increases; and generating a first transition probability matrix indicating probabilities of visiting the web pages using links; and applying a page ranking algorithm to the first web graph to generate a first ranking of the web pages based on the first transition probability matrix and the first jumping vector wherein the ranking of a suspected spam web page is lowered as a result of setting the probability of visiting the suspect spam web page without using a link based on confidence that the suspected web page is actually spam; and determining by the computing device a second ranking of the web pages based on the second web graph and the first ranking of the web pages based on the first web graph by: initializing a second jumping vector indicating probabilities of visiting the web pages without using a link, the second jumping vector being initialized based on the first ranking of web pages such that a higher first ranking increases the probability of visiting a web page without a link; and generating a second transition probability matrix indicating probabilities of visiting the web pages using links; and applying a page ranking algorithm to the second web graph to generate a second ranking of the web pages based on the second transition probability matrix and the second jumping vector.
6. A computer-readable storage medium containing instructions for controlling a computing device to rank web pages, by a method comprising: providing a first web graph representing links between the web pages at a first time and a second web graph representing links between the web pages at a second time that is later than the first time; determining a first ranking of the web pages based on the first web graph by: initializing a first jumping vector to indicate probabilities of visiting the web pages without using a link, the initializing including setting the probability of visiting a suspected spam web page without using a link based on confidence that the suspected spam web page is actually spam so that the set probability decreases as the confidence increases; and generating a first transition probability matrix indicating probabilities of visiting the web pages using links; and applying a page ranking algorithm to the first web graph to generate a first ranking of the web pages based on the first transition probability matrix and the first jumping vector wherein the ranking of a suspected spam web page is lowered as a result of setting the probability of visiting the suspect spam web page without using a link based on confidence that the suspected web page is actually spam; and determining by the computing device a second ranking of the web pages based on the second web graph and the first ranking of the web pages based on the first web graph by: initializing a second jumping vector indicating probabilities of visiting the web pages without using a link, the second jumping vector being initialized based on the first ranking of web pages such that a higher first ranking increases the probability of visiting a web page without a link; and generating a second transition probability matrix indicating probabilities of visiting the web pages using links; and applying a page ranking algorithm to the second web graph to generate a second ranking of the web pages based on the second transition probability matrix and the second jumping vector. 7. The computer-readable storage medium of claim 6 wherein: the providing includes providing a first and a second transition probability distribution indicating probability of transitioning from one web page to another web page using a link; the determining of the first ranking includes determining a first stationary probability distribution based on the first transition probability distribution indicating a stationary probability of transitioning to each web page; and the determining of the second ranking includes determining a second stationary probability distribution based on the second transition probability distribution and the first stationary probability distribution wherein the second stationary probability distribution represents the second ranking of the web pages.