The city had shut down parts of its network while its Information technology department worked to investigate "the scope and severity" of the digital attack that began Wednesday evening, according to a statement posted Friday on the city website.
The city said ransomware was to blame for the digital breach. The software is frequently used to extort money from governments and other targets by threatening to publish confidential data or block access to files, with attacks on the rise in recent years.
The attack had not impacted "core functions" including "911, financial data, and fire and emergency resources," according to the city's statement.
But the attack had prevented some residents from filing police reports, and the Oakland Police Department said via email it did not have access to certain case files due to the breach. The department's strategic communications manager Paul Chambers declined to comment when reached by phone Monday and referred all questions to the city.
Mayor Sheng Thao's office declined to comment on the cause, referring questions to the city administrator, who did not immediately respond.
"Some folks have not been able to pay taxes or use city services," District 6 Councilmember Kevin Jenkins said when reached by phone Monday afternoon.
Information technology workers moved some city systems offline as they attempted to restore services, the city's statement said. In the meantime, "the public should expect delays."
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