The Oakland Information Technology Department (ITD) said it is coordinating with law enforcement and actively investigating the scope and severity of the issue.
"The city is following industry best practices and developing a response plan to address the issue," the Friday statement on the city's website said. "In an abundance of caution, ITD has taken affected systems offline while they work to secure and restore services safely."
The public should expect delays from the city as a result, the statement added.
"This ransomware attack has not impacted the Oakland Police Department’s ability to receive and respond to 911 emergency calls," the department said in a press release. "Members of the public can also complete online crime reports."