What Operating System are you using? Also helps if you define what is 'they' with some detail.
Without knowing your OS I can't give you the steps, but most likely you will know if you can boot into Safe Mode and how (SM w/networking); boot into safe mode and run virus scans while in safe mode w/ networking, networking where you can download virus scanners such as Malwarebytes and etc.
Taking a wild guess by 'they' you mean some vicious virus??