Alert to the Computer on the network

[Interface]

Hi,

Is there a product or any way or scrept to

1. Detect and send alert to the Computer which is plugged in the network with out informing the authority.

2. Send a warning message automatically and immediately to the PC and block the newly connected PC to access the network resources, when it is connected to the network.

The warning message should look like a legal notice to inform the person to contact the system department for the permission to connect the PC to the network.