New
#11
Microsoft Security Essentials is utter crap and is just a baseline scanner, ditch it, don't use it, and don't trust it. Install something like Bitdefender Free. Now scan you computer with Herdprotect portable and research what it finds. Run Autoruns, go to File and post the ARN file. You'll need to zip it to upload here.
You may also want to scan your computer with a live CD such as Bitdefender Rescue disk.
If you do have malware and it's polymorphic then you more than likely won't find it with a definition-based anti-virus. In this case, backup your stuff, format and reinstall Windows.
Have a gander at Sandboxie for your browser. It's free for the browser, but after around 30 days when you launch Sandboxie it will present you with its license manager making you wait 5 seconds to launch your browser in Sandboxie. Small price to pay for free. I use the free version myself. Sandboxie keeps data in a sandbox environment and doesn't touch your computer unless you recover it. So be mindful at what you allow to be recovered.
Scan all downloads at Virus Total. I can't stress this enough.
Links:
Download Portable herdProtect 1.0.3.9 Beta
Autoruns for Windows - Windows Sysinternals | Microsoft Docs
How to create a Bitdefender Rescue CD