An anti-theft device, for securing an electronic product during retail display, having a socket for the transmission of power and/or information during normal operation, and a plug for engagement with the socket. The plug has an insertable portion, for insertion into the socket, with a lock to prevent removal while locked. The insertable portion also has a release enabling for withdrawal of the insertable portion. The plug has a control mechanism for holding the lock when the plug is engaged with the socket, the lock can be changed from a locking to release configuration by operation of a security key. The device also includes a flexible attachment for attaching the plug to a fixture. In one case the insertable portion includes a pin with an expandable tip for locking the pin to the socket. The flexible attachment may include conductive wires and be joined to an additional electric connector.