Birmingham Mayor Randall Woodfin’s office today confirmed that the city’s computer systems were attacked nearly a month ago.

In a memo sent to city employees this afternoon, Woodfin’s office provided a brief update on the network disruption, and acknowledged for the first time that hackers accessed the city’s computer systems. AL.com obtained a copy of the memo.

“This process is ongoing; however, based on the investigation thus far, we understand that an unknown third party gained access to our systems for a period of time,” according to the memo sent to employees by Rick Journey, the mayor’s communications director.

Officials said the problems began on March 6 when they observed unexpected activity that disrupted operations of some computer systems.

“Upon learning of the unexpected activity, we took steps to confirm the security of our network,” the memo reads. “We are working to restore full functionality to our systems as soon as possible.”

Journey declined to comment on the memo for this article.

“As our investigation into the activity causing the network disruption remains ongoing, we are unable to provide further details at this time,” Journey told AL.com.

The mayor’s memo to city employees comes a day after AL.com reported that the city had been the victim of a ransomware attack by hackers.

Earlier today, AL.com emailed the city a list of questions about employee concerns about whether they are being paid accurately, as they are not receiving pay stubs. Journey said the city would work to provide detailed responses to those questions.

In the memo, city officials reiterated their earlier statements that employees will continue to get paid.

“As previously stated, payroll will continue as scheduled and payroll coordinators will work with the departments of finance and human resources to address any individual questions or concerns you may have,” the memo states.

AL.com reported on Tuesday that the network outage has forced employees to use pen and paper for time sheets.

The memo noted that the city has been working with third-party specialists to investigate the disruption and its impact.

“Critical public safety and public works services have been uninterrupted. We want to thank you and each of your departments and divisions for establishing ways to continue services for our city,” the memo reads.

Multiple government sources have told AL.com that the city is the victim of a ransomware attack, with hackers gaining access to the city’s computer systems and demanding payment for the city to get its data back.

City officials have stressed that the 911 system has not been affected. Emergency operations remain functional.

However, the computer hack has caused some problems for law enforcement with police facing limitations on checking to see if a vehicle has been reported stolen or if a person has outstanding warrants, AL.com has reported.

AL.com reporter Carol Robinson contributed to this report.