and that's what's really being used to target. >> ifill: eitan hersh, how long has this been going on. >> tarring using photo registration has been going on for a long time, for a century. it really got off the ground in a serious way after the help america vote act which is in response to our election troubles in the year 2004 for states to start making digital up regulated voter files. making those voter files at the state level the campaigns caught on that they could start assembling massive databases by linking people with their birth dates, address and personal information with all sorts of commercial and other public records. >> ifill: let me ask you this. i'm a bob marley fan but i also like pat boone is this telling anyone out there who wants to get elected who i'm likely to vote for. >> maybe not. one thing about mar crow targeting they have these campaign parties that's not correlated with your political disposition. just because you listen to those musicians doesn't really mean that those dispositions towards music are correlated with dispositions that campaigns care about,