Undetectable interception of network traffic on LAN technologies

Nowadays it's impossible to imagine a company that doesn't use Internet and Intranet (LAN) to move confidential data around. Safety measures can be both: hardware and software information security solutions. The cases of development and usage of custom, their own systems of automation of information processing (electronic document management, accounting, backup, etc.) are not rare, any more. In that case information security department assess the sustainability of computer networks or systems to attacks by the software, forgetting the data that being transmitted over the Ethernet (except, perhaps, Wi-Fi channel, but they only checking for cryptographically strong algorithm and a password). In current article, we propose a concept of the device for not-detectable interception (and modification) of the transmitted information through the Ethernet network.