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DALLAS (CBSDFW.COM) – Dallas City Manager T.C. Broadnax told the Mayor and City Council Monday, staff continues to test the outdoor warning siren system after it was hacked late Friday night.

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The testing uses tools that does not involve activating the sirens so residents should not hear the sirens unless there is an actual warning.

“We believe that the City’s siren system was compromised Friday night,” Broadnax said in a statement. “For security reasons, we cannot discuss the details of how this was done, but we believe it came from the Dallas area. We are taking Friday night’s incident very seriously.”

Broadnax said he has also begun to look at critical systems city-wide to see what, if any vulnerabilities exist.

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These include the water system, radio network, 911/311, police-fire dispatch, flood warning system, financial systems and more.

Broadnax said his staff will come back to the City Council Wednesday with an action item and a plan to move forward with these assessments.

“Over the weekend, after extensive consultation and discussions with siren engineers, the city has implemented several improvements to prevent this from happening again. We have added extra encryption and other security measures to the system,” the statement said.

Dallas Police and the FBI continue to investigate what happened Friday night.

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I want to stress that the city’s warning siren system is fully operational,” said Broadnax. “We are asking the public to refrain from calling 911 or 311 if they hear siren activity. If the sirens are activated for any reason, information will be posted on the City’s social media channels.”