The data of nearly 200 million registered US voters were leaked online.
The Monday leak was discovered by security firm UpGuard, which said the data came from three analytics companies hired by the Republican Party, reports Xinhua news agency.
Names, birth dates, addresses and other voter registration details of some 198 million voters were leaked, according to UpGuard.
The number of overall US registered voters is just over 200 million.
The 1.1 terabytes of data was discovered on June 12 in an 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.
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