Once, my friend asked me to fix his computer. It was working very slowly - 100% CPU most of the time. There were a lot of pop-up ads and unknown processes.
However, antivirus programs did not find any threats.
I found a deep hidden program, cheating his antivirus. This program is known as a Rootkit (undetectable virus).
I created UnHackMe to remove Rootkits easily. That was in 2005!
Now UnHackMe eliminates most types of malicious software.
UnHackMe is really best at fixing the issues, which antivirus programs do not.
Modern virus creators use FILELESS MALWARE. Fileless viruses do not create or change your files.
They live in the Windows registry, WMI, shortcuts, and scheduled tasks. Sometimes virus is just the URL of a malicious web site.
Antiviruses are good at fixing viruses in files, but they can not help detect or fix Fileless malware.