The environmental regulator Sepa says criminals are demanding a ransom to unlock its digital systems which have been subjected to a cyber attack since Christmas Eve.
It said international groups were likely to be behind the ransomware attack that has locked its emails and contacts centre.
More than 1GB of data has been stolen, including information about staff.
Police Scotland and the National Cyber Security Centre are investigating.
Sepa (Scottish Environment Protection Agency) said it was likely that new systems would have to be built from scratch.
Critical services, such as flood forecasting, are not affected.