About 500 computers in county Behavioral Health and Recovery Services were compromised by the cyberattack Tuesday, according to a press release issued Friday.
A message popping up on screens asked for a ransom amount in exchange for releasing control of the computers.
“When they tried to open the files they were white, blank or corrupted,” County Spokeswoman Amy Vickery said.
The hackers demanded about $65,000 in bitcoin ransom.
The Sheriff's Department is working with the FBI to investigate the cyberterrorism. The county had no information on the origin of the cyberattack.
The county does not intend to pay the ransom and was working to restore the computer network used by BHRS.
"Our staff is confident that with the strategy they have identified, they will be able to restore the systems back to operation ideally by Monday,” Vickery said.
It's believed to be the first time county offices have been victimized by ransomware hackers.
The BHRS computer network was shut down earlier in the week and staff were using paper documents in working with clients. No breach of personal information has been detected at this time, the county said.
Vickery said staff continued to see clients at the 24 locations of BHRS and the phones were working.
The county department with more than 400 employees provides services for about 14,000 adults and children, including mental health services and help with overcoming addictions.
According to the news release, the county has security measures that have averted ransomware attacks in the past, but the hacking techniques in this attack got past the security systems.
Following Tuesday's attack, the affected computer network was isolated from the larger network used by county offices. Temporary arrangements were made for online services and communication, and the county encouraged clients to keep their appointments.
BHRS clients may call the county's 24-hour Emergency Support Service line at 209-558-4600.