Since you've already run Malwarebytes & Defender, if you suspect you have an infection, I would suggest you try these scanners & see what they find.
You may wish to run this program before you do a scan with your malware scanners.
As RKill only terminates a program's running process, and does not delete any files, after running it you should not reboot your computer as any malware processes that are configured to start automatically will just be started again.
Instead, after running RKill you should immediately scan your computer using some sort of anti-malware or anti-virus program so that the infections can be properly removed.
TDSSKiller (Rootkit scanner)
is a program that searches for and deletes Adware, Toolbars, Potentially Unwanted Programs (PUP), and browser Hijackers from your computer. By using AdwCleaner you can easily remove many of these types of programs for a better user experience on your computer and while browsing the web.
TDSSKiller is a utility created by Kaspersky Labs that is designed to remove the TDSS rootkit. This rootkit is know under other names such as Rootkit.Win32.TDSS, Tidserv, TDSServ, and Alureon. TDSSKiller will also attempt to remove other rootkits such as the ZeroAccess or ZeroAccess rootkit if it is detected.
When running TDSSKiller, launch the program, click on the blue text "Change Parameters" & check the box marked "Detect TDLFS File system." Click OK & then run the scan.