You should check your OS build to verify you're running the lastest version available. I'd recommend complementing Windows Defender built-in antivirus with Comodo Firewall in order to have more control over the system (HIPS, SandBox, inbound/outbound connections). Good on-demand scanners are Zemana AntiMalware, Norton Power Eraser, Emsisoft Emergency Kit, for example.
Thanks for sharing.