Urgent Warning

This router is perfect. Functionality, signal strength, power - all the best. I have connected a 2TB USB disk on which all media files are stored, to be accessed centrally (music, videos, etc.). The WLAN is secured with a password - I thought! Yesterday, an acquaintance made with his I-pad to search for a network in our apartment. He found the encrypted 2.4 GHz wireless network and to my great surprise, an open ASUS 5G WiFi, namely from my router. For two months, so the 5 GHz range was open like a barn door without my knowledge. So I can only advise everyone urgently, to check the tab 5GHz once the wizard for the wireless LAN setup. I bet that very many users find that they too have forgiven neither its own SSID and password were here.