Shares of Comscore (SCOR) plunged 22.5% on news of Google's competitor Ad Planner service [1]. The company even scheduled a conference call the following day to address the issue [2].
While Comscore's data suggested that Google was having a weak quarter, GOOG's street-beating quarter lead investors to believe that Comscore's data was becoming less reliable and would result in lower revenue. However, Comscore countered this argument by attempting to show that the data was "misinterpreted." [1]