A user browses to a website.

A website that is not secure means that the connection between the user’s browser and the web server is not encrypted or authenticated. This can expose the user’s data to interception, modification, or impersonation by attackers. One way to secure a website is to use HTTPS (Hypertext Transfer Protocol Secure), which is a protocol that encrypts and verifies the data exchanged between the browser and the server. HTTPS relies on certificates, which are digital documents that contain information about the identity and public key of the website owner. Certificates are issued by trusted authorities called certificate authorities (CAs), which verify the legitimacy of the website owner before issuing a certificate. When a user browses to a website that uses HTTPS, the browser checks the certificate to ensure that it is valid, signed by a CA, and matches the website’s domain name. If any of these checks fail, the browser will display a warning message that the site is not secure, and advise the user not to proceed or enter any sensitive information.