(CNN) Atlanta's mayor on Thursday urged anyone with personal information in city information systems to check their financial records as an investigation continues into a ransomware attack on the city.

Ransomware is a malicious software that prevents or limits users from accessing their system by locking them out until a ransom is paid. NBC affiliate WXIA reported that the city received a ransom demand in bitcoin for $6,800 per unit or $51,000 to unlock the entire system. CNN has not independently confirmed the report.

Mayor Keisha Lance Bottoms advised city employees to contact credit agencies and monitor their bank accounts in case their personal data was compromised. She urged the public to take the same precautions while investigators work to determine the scope of the attack.

"We don't know the extent so we just ask that you be vigilant," Bottoms said in a Thursday news conference. "All of us are subject to this attack, if you will. Many of us pay our bills online, we have direct deposit, so go online and check your bank statements."

Atlanta Chief Operating Officer Richard Cox confirmed that the city received a written demand related to the attack. When asked in the news conference if the city was going to pay a ransom, Bottoms said, "We can't speak to that right now."

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