Formatting client machines

Hello,

I'm working on a pilot for a customer and I received a question about the way SEP Manager console identifies the client machines.

The customer is asking what happens if  you format a machine with the client installed and then reinstall the agent.

More in deep, which is the unique identifier that the SEP Manager uses to identify a client machine? Is the IP Address, the hostname or the MAC Address?

Thanks in advance.

Best regards,

Alex.