Occasionally Windows reports that Internet Security is disabled. I am unable to get it re-enabled through the settings and the only way I have found to get it working again is to re-install. This is Windows 10 64bit with Maximum Security 2017
Thanks for asking here @fhoare, and welcome to the community!
One possible reason why you are getting a Protection disabled messages is that there is a conflicting software on your computer that is causing the Trend Micro program to be disabled, or you have a Potentially Unwanted Application installed. These Potentially Unwanted Applications piggyback or is bundled to a legitimate program and users are tricked into installing them as they will advertise that it can boost or safe guard your computer. You must check your computer if there are programs installed without your permission. You can also click on this link for you to check the list of conflicting programs that can disable the Trend Micro program.