Question Author
Thank you all for your advice.
My laptop sits on the table. I usually put a book under it to lift it up from the surface. I can't remember when I bought it but it must be at least six years old. I do have a new laptop but tend to use this one more often as it's usually easier to navigate.
I shall go and get a screwdriver and take the back off and have a look inside later today, when I'm more awake.
Togo, the only security programme I have installed is AVG. I run Malwarebytes, now and again, and also CCleaner.