Theory Test Pro uses a secure connection on the internet, https://. The 's' indicates the secure link. However, during the time when our website certificate renews you may get an error message 'This is not a secure link' when you attempt to sign into your account. You can click on the little open padlock to view the details of why the connection is not secure. It will say something to the effect that our certificate has expired.
If you experience this it is likely that an old version of the site is being held in your browser history. This will usually sort itself out in time but you can sort it immediately by clearing your browser cache.