The invention relates to a security module for connection to an automation device or automation system, which is provided for the control of safety-critical and non-safety-critical processes and/or system components, comprising a communication board (LP1), the processing unit (14) of which can be connected to a central unit (CL) via an input/output bus slave (12) and an external input/output bus (IOB1) connected thereto. The communication board (LP1) comprises a serial communication master (10) connected via at least one communication link (IKB1), which can be connected to said communication master, to one or more secure processing units (24), (34) arranged on one or more printed circuit boards (LSP1), (LSP2) having safety-related input/output circuits (23), (33) for safety-related functions so that at least one of the printed circuit boards (LSP1), (LSP2) is provided to receive the telegrammes sent by the communication board. An internal communication slave (20), (30) is provided on the printed circuit boards (LSP1), (LSP2) for safety-relevant functions, which can be connected to the serial communication master (10) via the internal communication link (IKB1), (IKB2). Safety-related telegrammes can only be transmitted from and/or to the processing unit (14) of the communication board (LP1) via one of the secure processing units (24) which are located on teh printed circuit boards (LSP1), (LSP2) for the safety-related functions by means of at least one second internal communication link (IKB2).