The Pennsylvania Senate Democrats have been hit by a ransomware attack that has locked senators and employees out of their computer network since the early morning hours of Friday, state officials told NBC News.

In a statement, Sen. Jay Costa, the Democratic leader, said the Democrats were working with law enforcement agencies and Microsoft to resolve the problem. He did not say what payment has been demanded to unlock the data, or whether the attackers had suggested any political motive.

In a ransomware attack, hackers inject a network with malware that typically encrypts important data, and then demand payment in exchange for a key that releases the data. They threaten to destroy the data if they aren't paid.

The Democratic senators in the state capital of Harrisburg are on their own computer network and there is no indication that other state agencies of the Republicans have been affected, said a state official who declined to be identified. The official said the Democrats had no idea whether they were targeted for any specific reason.

A spokeswoman for the FBI was looking into whether that agency had been called in. A spokeswoman for the Pennsylvania Democrats, Stacey Witalec, declined to say whether the data was backed up elsewhere or whether the attackers had identified themselves or any motive.