You need to resecure your router.
Using an Ethernet cable connect to your router at 192.168.1.1
1. Turn of the Wifi in the settings until you have finished making changes. This will prevent someone from spying on you during the process. Also unplug any Ethernet cables plugged into your router except the cable you are connected using.
2. Change the admin password for your router to something secure. At least 10 characters including capital letters, numbers and special symbols. You will then need to resign back into your router.
3. Change the SSID for your WiFi radio.
4. Enable WPA2 security. Use an encryption phrase of at least 12 characters and again with Caps, Numbers and special characters.
5. Turn WiFi back on and reconnect and cables that you disconnected.
Then using the new paraphrase reconnect your various wireless devices to the network. Tell you kids not share the paraphrase with friends.
It may take 24 hours for clients to drop off the list of DHCP clients as the router is still reserving an IP for them, but they are not connected.
A few more advanced things you could do for security;
1. Verify that administrative from the WAN is blocked (this is default )
2. Set up automatic timers on the router to shut down WiFI radios at night and then turn them back on in the morning.
3. I don't remember if WPS can be turned off on the Actiontec but if it can turn it off.
If you still have strange devices logging on then your network has been hacked
Cable boxes are not connected using WiFi.
Cable boxes will be listed as connected over coax. Some models of cable box will have two connections per box. Cable boxes usually have are assigned IP addresses starting at 192.168.1.100.
When you're connected to the router, you can visit the advanced stats on the system monitoring page to view the bandwidth usage. This can help you detect when internet traffic is active.
Good Luck.
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