If a computer behaves oddly, even with av products, I use the free Kaspersky onlive virus cleaner to check the computer really is clean. It has caught and disinfected really nasty stuff - like the ransomware that encrypted my photos and music. The paid for products do provide better overall protection as they are not just antivirus products but are also firewalls and anti malware. Also, do you realise that Kaspersky offer a free version of their product? This gets the best ratings from all the free av products. https://www.kaspersky.co.uk/free-antivirus
Particularly popular in Salisbury.
Used to get it free with my bank but they stopped it this year due to Russian spy wear thing. Was offered it for special price of £5 but decided on another freebie. Was fine when we had it for years. No issues
Great find OP. Head added. One of the best security software available