The FBI is investigating a ransomware attack on the city of Atlanta

Personal information of Atlanta residents may have been compromised, Mayor Keisha Lance Bottoms said. She advised city employees to contact their respective credit agencies and monitor their bank accounts in case their personal data was compromised. The city's payroll has not been affected.

"This is a very serious situation," she said. "We don't know the extent, so I would ask for people to assume that you may be included."

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.

City officials learned of the attack at 5:40 a.m. Thursday, Cox said. Some city data remains encrypted while investigators continue to determine the scope of the attack. Microsoft and Cisco are assisting the investigation.

The city's airport and water systems were not affected, Cox said. Officials have yet to decide if City Hall will be open Friday.