If they’re installing an antenna to your router, that means that it creates a “rogue wireless” often used by mobile devices signed to that company when they’re on the road.
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Though this type of setup tends to be segregated from your network, it still creates an attack vector and also means that any third party could use your network/IP as a launchpad for a nefarious act.
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Simple advice, disconnect the antenna from your router, and demand that they disable the ‘rogue network’ preconfigured in the router.
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