(CNN) -- The Federal Bureau of Investigation and Department of Homeland Security are investigating a ransomware attack on the city of Atlanta, city officials said Thursday.
The cyberattack affected external and customer-facing applications, including those used to pay bills and access court-related information, Atlanta Chief Operating Officer Richard Cox said at a news conference. The city's payroll has not been affected.
City officials learned of the attack at 5:40 a.m. Thursday, Cox said. Several departments were affected but public safety and water services are operating without incident, he said.
Some city data remains encrypted while investigators continue to determine the scope of the attack. Microsoft and Cisco are assisting the investigation, he said.
Mayor Keisha Lance Bottoms advised the public to be "vigilant" as investigators work to determine the extent of the breach.
She advised city employees to contact their respective credit agencies and monitor their bank accounts in case their personal data was compromised.
"We don't know if it's limited to information related to just our employees or if it's more extensive than that," Bottoms said in a Thursday news conference.
"But because we don't know I think that it would be appropriate for the public just to be vigilant in checking their account and making sure your credit agencies also have been notified."
Officials have yet to decide if City Hall will be open Friday.
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