SIOUX CITY, Iowa (AP) — The Woodbury County Board of Supervisors has approved an investigation into a cyberattack that compromised about 3,700 county files last month. The Sioux City Journal reports that the board voted unanimously Tuesday to work with Cleveland-based law firm BakerHostetler, which conducts data security incident response investigations.

Human resources director Ed Gilliland says the source of the cyberattack July 20 was ransomware that was delivered through an email. Ransomware is software that locks files on a computer and demands a payment for their release. Gilliland says nothing was lost because the Woodbury County Information Communication Committee backs up files every night. Emails requesting ransom for the files have been deleted.

Gilliland says the investigation will help determine which specific files were targeted and whether there will be any long-term consequences.