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Check the SSL certificate your browser shows you against the [logged SSL certificate](https://crt.sh/?CN=*.trezor.io&exclude=expired&deduplicate=Y) and ensure yours is one of the logged ones. If it isn’t your VPN, or some other software is performing a de-SSL on your traffic (really bad).
I’ve seen this commonly done in corporate and university networks. A big clue is if your ISP or VPN requires you to install a certificate, this could be a red flag.
Anyway, back on topic, if your current root CA does not trust the CA of your SSL cert you will get this message. This distrust can happen for any of the following reasons:
1. Someone is doing a de-SSL and you didn’t update their de-SSL certificate.
2. Your OS is out of date and you are missing a Root Cert update
3. Your Browser is out of date and missing a Root Cert update
Good luck.