I'd also run Malwarebytes or any other anti-virus solftware you may have, this sounds like a virus to me tbh. Also what OS are you using ? Win 7 Ultimate, which I use averages 1.5-2GBs *and like you doesn't show in taskmanager*.
I also have 12GBs of ram, but I also run Advanced system care pro, which has a little app that free's up ram. I also noticed that after using apps that use a lot of ram *like handbrake* that my in use ram go's way down, sometime's below 1GB *wish it was always like that lols*. Hope some of this helps