Deutsche Bank is involved in a probe into possible criminal wrongdoing after it hired detectives to carry out surveillance of some board members in the latest in a series of spying scandals at top German companies.

Data protection authorities in the bank's home state of Hesse have asked prosecutors to establish whether to open a criminal investigation, two months after the bank revealed it would ask external lawyers to investigate the activities of its own corporate security department.

Deutsche has terminated the contracts of two people, including its head investor relations chief, as it continues its inquiry into possible unauthorised surveillance of board members and investors. The affair risks the reputation of the bank, not least in Germany, where corporate snooping and unauthorised use of data are viewed with particular hostility. It is also an unwelcome distraction for Josef Ackermann, chief executive.