A Facebook post for staff said: "The information included names, addresses and bank account details of colleagues. This affects colleagues from all levels of the organisation.
"We are taking this extremely seriously. Dalton Philips is leading the response."
But one person commented on the site: "I haven't been informed of this and shouldn't have to read it on here."
More top news
Councillors are hoping threats of court action and fines will change the habits of rogue rubbish dumpers.
Rebez Saleh denied the three counts of possession with intent to supply class A drugs but was found guilty at Sheffield Crown Court.
Jon Mitchell has Friday's early morning forecast.