The detailed data of nearly 200 million U.S. registered voters were leaked online, local media reported on Monday.
The leak was discovered by security firm UpGuard, which said the data came from three analytics companies hired by the Republican Party.
Names, birth dates, addresses and other voter registration details of some 198 million voters were leaked, according to UpGuard. The number of overall U.S. registered voters was just over 200 million.
The 1.1 terabytes of data were discovered on June 12 in a unprotected cache on the Internet, but secured by June 14.
Deep Root, a company involved in leaking the information, said the data was exposed on June 1 after a system update.
The leaked info exposed the extent to which U.S. political entities analyzed voter behaviors in order to capitalize on predictions made on the basis of those analysis.