Authorities are investigating the source of a cyber attack against four New Jersey Internet gambling sites by a hacker who threatened more of the same unless a ransom was paid using the online currency Bitcoin.

David Rebuck, director of the New Jersey Gaming Enforcement Division, says last Thursday's attack lasted about 30 minutes. It involved an attack that flooded the sites with information, rendering them inoperative.

The attacker promised a more powerful and sustained attack within 24 hours if the ransom was not paid, but no further attacks were reported.

Rebuck did not identify the sites that were affected nor the size of the ransom sought. But he said numerous local and state law enforcement agencies are investigating.

No player money was stolen and no personal information was compromised.