Symptoms
- Warning page before the site loads mentioning a certificate problem
- Padlock icon missing or showing a warning in the address bar
- Message about the connection not being private
- Warning only appears on one specific site
Likely causes
- CommonExpired or misconfigured website certificateThe site owner's security certificate has lapsed or was set up incorrectly.
- CommonIncorrect date and time on your computerA wrong system clock can make valid certificates appear expired or invalid.
- PossiblePublic Wi-Fi intercepting trafficSome public networks perform traffic inspection that can trigger certificate warnings.
- Less commonActual man-in-the-middle attackIn rare cases, the warning reflects a genuine attempt to intercept your connection.
What to do
- Check your computer's date and time settings and correct them if wrong.
- Avoid entering any personal information or passwords while the warning is showing.
- Try loading the site on a different network, such as switching from public Wi-Fi to your home network.
- Try a different browser or device to see if the warning is specific to one setup.
- If the warning persists across networks and devices, avoid the site until the owner fixes the certificate.
- Contact the website owner if you know them, since they may not be aware of the expired certificate.
- Never click through a certificate warning on a site handling sensitive information like banking or shopping.
When to call a pro
If you suspect active interception on a public network rather than a simple expired certificate, avoid sensitive activity on that network entirely.
Safety
Use caution
Do not enter passwords, payment details, or personal information on a site showing a certificate or 'not secure' warning until the cause is confirmed safe.