Dealing With Expired Certificates
When you visit a website, you may encounter a warning message before the site loads, saying something similar to This Security Certificate Has Expired. Unless you know for certain the error is on your computer, do not continue to the website. Some problems occur on the user side due to a lack of certificate updates or incorrect settings (for more information on fixing that, check the linked article).
An expired certificate more likely means the site has not renewed their certificate though. This can be just a simple lapse on the site owner's part, or something major, such as someone hacking the site. Even if the https appears, if you receive any message that the certificate has expired, give the site some time to renew their certificate before revisiting.
Any data you submit or receive from the site will not be encrypted. There is also no authentication to ensure you are actually working with the site itself and not a third party posing as the website. Information can easily be redirected to a third party without a certificate.
You should never change your browser settings to ignore certificate settings. This is your first line of defense against fraudulent websites. At the very least, ensure your settings display messages about expired security certificates.
Image Credits: Security Certificate Warning Message / Internet Explorer