What is the way to atone for money acquired through illicit means, and how can one avoid returning to such actions in the future after repentance?

All public funds taken must be returned, for the Prophet, peace and blessings be upon him, said: "The hand is responsible for what it has taken until it returns it." This should be accompanied by remorse, seeking forgiveness, and a firm resolve not to repeat the act. If exposure is feared, the money can be returned via an anonymous transfer, or spent for public benefit if it is impossible to return it to the institution or if there is a fear of it being embezzled again.