This paper provides a quantitative approach to measuring the effectiveness of ambush marketing by using Google data. To our knowledge, it is one of the first studies that develop an empirical approach that directly measures the attention effect of ambush marketing in sports. The new data consists of 14 ambushers (treatment group) and 26 official sponsors (control group) and covers the time period of 2004 to 2012. These firms conducted marketing activities during the past football World Cups and European Championships. The innovation in our paper is the measurement method of attention by means of Google. The results are as follows: First ambush marketing increases product attention significantly. Second the product awareness of ambushers is greater or the same to that of official sponsors. Finally, we demonstrate that ambush marketing has positive impacts on the company's performance. Overall, we conclude that Google provide new insights for the analysis of ambush marketing.