If, when opening a website, your browser displays a ‘Your connection is not private’ warning (Chrome, Edge) or, in Firefox, a page warning of a security risk, this means that the browser was unable to verify the website’s SSL certificate. In such cases, it is not certain that you are actually communicating with the server you intend to, which is why the browser does not automatically load the page.

The error code indicates the cause

An error code also appears beneath the warning (in Chrome, by clicking the ‘Advanced’ button):

Error code	Meaning
NET::ERR_CERT_DATE_INVALID	The certificate has expired, or the system clock is out of sync
NET::ERR_CERT_COMMON_NAME_INVALID	The certificate is not valid for this domain (or the www. version)
NET::ERR_CERT_AUTHORITY_INVALID, SEC_ERROR_UNKNOWN_ISSUER	Self-signed certificate, or intermediate certificate missing
ERR_SSL_PROTOCOL_ERROR	The server is responding with an incorrect or outdated protocol

As a website owner: here’s how you can fix it

1. Check the certificate details: click on ‘Not secure’ in the address bar, then click on ‘Certificate details’. You can see who it was issued to, who issued it, and how long it is valid for. It’s quicker to enter the domain into our free SSL checker: in a single step, it shows you whether the certificate is valid, when it expires, which names it covers, and whether the certificate chain is complete. You can enter multiple addresses at once (for example, pelda.hu, www.pelda.hu), so you’ll also find out if only one of the variants is incorrect. Further methods for checking expiry dates are described in the article on checking certificate expiry dates.
2. Expired certificate: Let’s Encrypt certificates are renewed automatically; if this has not happened, the article on AutoSSL errors will help you identify the cause. For paid certificates, renewal is not automatic; you can find the steps to follow in the article on renewing paid certificates.
3. Invalid domain: the certificate must be valid for both versions of the domain (pelda.hu and www.pelda.hu) and for all subdomains in use.
4. Missing intermediate certificate: if the page displays an error in certain browsers or on certain mobile phones but not elsewhere, a component of the certificate chain is likely missing; installing the CA bundle will resolve this.

Mixed content does not cause this warning; rather, it causes the padlock icon to disappear or the browser to display a ‘not fully secure’ message. The article on the mixed content error explains how to rectify this.

As a visitor: when should you continue?

You can also use the SSL checker to find out whether the error is occurring only on your computer: the tool retrieves the certificate not from your computer but from its own network, so if it appears valid there, the error is not on the website. In such cases, the most common causes are:

• Incorrect date or time on your computer: set up automatic time synchronisation.
• Public Wi-Fi login page: on hotel or airport networks, the network’s login page intercepts requests. Open a page beginning with http://, log in to the network, then try again.
• Antivirus HTTPS scanning: some antivirus programs scan traffic using their own certificate; if this is not working correctly, please update your antivirus software.

On banking, online shop or login pages, never proceed past the warning. If the page uses HSTS, the browser will not even allow you to proceed, precisely for your own protection.