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Ms Driscoll said the council's network security was constantly monitored through both a third party "as well as our own internal security".
"It was through this we identified the threat. We were able to isolate it."
The lockdown lasted most of the day.
Ms Driscoll said the threat, when successful, takes files and locks things down.
"Once it is locked in, you don't always get the files back but - because we isolated it so quickly - it didn't managed to get into the system."
The council's online services are back up and running.