Whilst looking up an install error online, somehow something got installed by Tweakbit ('PC Repair kit'). Didn't know at the time, but apparently a PUP/malware.
Immediately ran Malwarebytes (free) full scan, followed by Superantispyware (free) full scan, then Malwarebytes again to check, followed by Windows Defender (full scan). Also ran Adwcleaner a few times, to try and find all traces, and clean.
I'm not entirely sure all remnants are gone, or if there's anything else I can do. Having said that, any checks and help anyone can offer would be gratefully received, any additional programs to run. Can't see any damage like browser hi-jacks that's immediately apparent.
Thank you for anyone who would be willing to help.
Windows 10, 64-bit, Home edition.