An archival study is presented where we collected the most important events occurred between the days of the terrorist attack, on March 11th, and the general elections, on March 14th, some headlines in the press, and a summary of a study about participation in political forums in Internet. This first study provides some clues on the importance that interpersonal communication and opinion leaders may have had in the change of public opinion, and explains the social context of the second study. Study 2 analyses, in a sample of 100 students, the credibility of official and unofficial information on the terrorist attack, as well as the influence of this information on one’s vote. Following the social judgment theory, credibility of information depends on the ideology of the receptors. Right-wing participants believe that their vote has been influenced more by official information, while left-wing participants believe that their vote has been influenced more by unofficial information. For those whose political tendencies are towards the centre there were no differences between the two kinds of information. Third-person effect (differential perception of the influence of information in self and others) is mediated by the kind of source, official or unofficial, and by political ideology