Patent ID: 8244722

Claim:
A method comprising: computing, by a processor, a first rank corresponding to a rank for a document at a first time; detecting, by the processor, a change in one or more ranking factors associated with the document during a transition period between the first time and a subsequent second time; computing, by the processor and based on the detected change in the one or more ranking factors associated with the document, a second rank corresponding to the rank for the document at the second time; selecting, by the processor, a rank transition function, from a plurality of rank transition functions, that corresponds to how the rank, for the document, changes from the first rank to the second rank over the transition period; calculating, by the processor and based on the selected rank transition function, a plurality of transition ranks that correspond, respectively, to the rank for the document during a plurality of different times in the transition period; estimating, by the processor and based on the plurality of transition ranks and the detected change in the one or more ranking factors, changes to the one or more ranking factors during the plurality of different times in the transition period; identifying, by the processor and based on the estimated changes in the one or more ranking factors, an indication of rank-manipulation during the transition period; and reducing, by the processor, the rank of the document at a third time that is subsequent to the first time and the second time, based on the indication of rank-manipulation.