Stupidly, of all things it was a recipe website that got me - it opened an unrelated page and I guess hit me when I clicked the button to close it. I've been running windows AV and it got straight through.
Anyway, lesson learned and I ran malwarebytes through the system first then did a factory reset. No way would I consider paying them for the key.
Following the reset, I still have the ransomware "theme" with wallpaper and colouring so I guess it must still be sitting somewhere. I've run an AV scan and it turned up nothing.
Laptop came with windows pre-installed so I can't do a format and reinstall as I don't have the dvd to do it.
Does anyone know where the remnants of this nasty thing might be sitting? Any ideas for another solution would be appreciated. I'm a bit worried a piece of this may be enough for it to crop up again.
cheers