In a device having data communication capability, a security method dynamically detecting a control connection, which originates from the device, and detecting a negotiation of a related connection within the control connection. The negotiation comprises at least defining a port of the device for said related connection. The method further checks if relationship between said port of the device and the control connection fulfills predefined criteria, and conditionally blocks said related connection, if said port of the device does not fulfill said predefined criteria. The method can be used for suppressing a vulnerability related to applets.