A socket (16) is designed to receive a plug of a pluggable device (14). The socket has a detection arrangement (42) for detecting connection of a plug to the socket. A new session identifier is generated each time a plug is connected to the socket and it remains valid while the plug remains attached. The session identifier is preferably generated mechanically (48) so that it can be generated without power to the socket or to the plug. This enables detection of system tampering of a system using the sockets.