Why do I have weak security showing under my WiFi carrier?

Because your router is configured to use a security protocol that is outdated and is no longer considered secure. Change the security settings on your router.

If the router was provided by your Internet service provider, and you don't know how to do it, I'd say you should contact them.

Check your WiFi Router / Modem for --> Recommended settings for Wi-Fi routers and access points ...

Consider more secure wifi configuration.

Change your router’s WiFi to use WPA2-AES (CCMP) with no WPA or TKIP. Updating this setting ensures that your devices always connect in one encryption mode

1. TKIP is obsolete and not considered secure. Choose WPA2, the latest encryption standard, with AES encryption for optimal security
2. If your router doesn’t specify TKIP or AES, the WPA2 option probably uses AES

See the pics below