Further instructions on how to use the Click here from Sea Urchin.
Use this link to remove Security Tool - don't use the downloads at the top of the page, but scroll down to the heading:
"Automated Removal Instructions for System Tool using Malwarebytes' Anti-Malware"
and follow the instructions very carefully. If you already have Malwarebytes you will need to download and install it again as per the instructions, as it's likely to have been compromised by the virus.
I hope the further instructions may help you sort out the problem if not already fixed.
I haven't run Malwarebytes but did a System Restore instead which appears to have done the trick. I've been on my computer for the past 3 hours with no disturbance from AV8, so hopefully, it wont return. If it does I've now got all the information to deal with it. Many thanks for all your help. I will tick as resolved.