A user encounters a website with a valid security certificate, but their web browser displays a warning that the website is not trusted. What is the most likely explanation for this scenario?
The Certificate Authority that issued the website's certificate is not trusted by the user's browser.
The website is using a self-signed certificate, which is not recognized by the user's browser.
The website is using a compromised certificate that has been revoked by the Certificate Authority.
The user's web browser is outdated and does not support the website's security protocols.
The website's security certificate is expired or invalid.