A control unit is described for technical installations, devices and/or machines having a microprocessor, a programmable memory and a housing enclosing the microprocessor and programmable memory. Data lines lead out of the housing for connection with an external device for writing data to the programmable memory. The control unit is enclosed in the housing such that the operability of the control unit is at least partly destroyed when the housing is opened. The control unit furthermore has a check device that checks for authorization a write access by which data are written to the programmable memory over the data line, and causes the data to be written to the programmable memory only in case of a successful check of authorization.