A couple suggestions to be a bit more discreet.

- Rename the application files to something other than XMR Stak, something obscure and generic like "system" "netsys" etc.... so if noticed by someone it won't be a dead give away on a Google search of "xmr stak" or even worse they know what XMR is, mining is popular you'd be surprised who is doing it.

- Run it as a scheduled task off hours, don't get greedy *edit "owner"

- Make sure anti-virus doesn't flag the software, this is a sure way to bring attention to the PC and applications running on it.

- Mine local pools as to not generate out of the country traffic that will look suspicious if it is big enough network to have advanced firewalls and net security.

Good luck, happy mining.