I had a Trojan virus. I am not actually sure what it was exactly called but I can tell you what happen when I got it.
The Trojan ate up my files and deleted some of my desktop icon. The very next day, things got worse, the virus infected 2 more files :|. From there, I knew that I am "fucked." I had Windows Defender to scan all my files but only to find that the Trojan was unable to detect.
The next thing I know, I had a fake anti-virus program running automatically. It made me defenseless, it blocked every .exe I click on. I had no choice but to reformat it.