You have picked-up Malware from somewhere and your Anti Virus programme is telling you so . It now needs to be removed and I suggest you download and run Malwarebytes.....the free edition Not the paid for one.
mrs_o....I think your Anti Virus is just stopping the malware from performing and the nastie continues lying 'dormant' in your computer. The malware now needs to be removed before it finds a way to avoid your Anti Virus programme. Consequently, if you were to scan with Malwarebytes you might have a surprise and find a lot of other nasties which need to be ousted.
Anti Virus discovers nasties and Malwarebytes will quarantine them prior to your removal of the items concened.