Abstract: A method for performing a safe guard detection of unexpected operations launched by an operator for a manufacturing execution system (MED system) is based on a first database containing a set of operations, a set of operators, calendar information for a shift and calendar information for the equipment of the MES-system. The MES-systems further has a second database containing a login history of carried out logins of the operator. The detection of a malicious operation is carried out as to whether the operation complies with a set of rules defining allowed operations or with a learning module, in which specific roles of operators are contained and whether an operation complies with a specific role. In case of non-compliance, the operation is stored as an entry in an event trace file for generating alerts.