I just saw this entry in the router logs. Notice the last entry 192.168.1.88

https://i.imgur.com/uCrx6ZN.png

1) The router's dhcp settings only give out ip addresses ending with 100 to 200. The means he tried to use a static ip address.
2) The mac address filter only allows a specific list of mac addresses to access the internet so had he chosen an ip address of 150, he would have needed to hack into the router admin panel as well to whitelist his machine.

The router is a TL-WR841N v13 00000013
Does anyone know any way I can further secure this thing besides changing the wifi password which I already did?
First of all this mac of 192 168 1 88 looks like Intel Corporate its a PC not a router please change your router password and change your wifi and keep monitoring your router.
@Prince, alright thank you. The password is now longer (21 chars) so it should be more difficult to crack (hopefully).
duke-of-bytes wroteIt doesn't look like a lot of activity
That is likely because he couldn't use the internet anyway because his mac address is not whitelisted.
My router admin user/password are both different that the stock ones so I suppose he was too lazy to crack those.
VincentKeyboard wrote@Prince, alright thank you. The password is now longer (21 chars) so it should be more difficult to crack (hopefully).
duke-of-bytes wroteIt doesn't look like a lot of activity
That is likely because he couldn't use the internet anyway because his mac address is not whitelisted.
My router admin user/password are both different that the stock ones so I suppose he was too lazy to crack those.
exactly .. so most probably it is only your wifi password that was compromised and not your router admin