Antivirus softwares are great. They protect you from active threats and can scan your system for them. But of course, there is a catch. And that is how slow they can make your system be, especially with older ones. Avast has been the most famous example for slowing down your system. And it's not by just a bit, since it's riddled with useless features (for most average users). Avira is a good example too, it literally comes with a whole fucking security suite but is also very, very hard to remove. This has seemed to be patched, but a few months before it was literally unremovable, uninstalling it and rebooting would make it appear again like it didn't want to uninstall at all. But as of many things out there, there is an alternative, which is...
It's currently December 2nd of 2020 as I'm writing this and Malwarebytes is still rocking. It only includes the essential features, and since 2016, never ever failed me once. Of course, it still has some caveats, like the software (not the detection engine or all that stuff) being closed source, meaning we can't know if it has hidden spyware or not. But it's still a very good solution even as of this date. Below you can see other useful software you might want to get for less dangerous threats.
You might consider getting these softwares to get rid of PUPs and (potential) malware :
AdwCleaner - Owned by Malwarebytes, it's a great to remove adware, PUPs or even potential malware. It's a great tool and alternative to SUPERAntiSpyware since AdwCleaner has one detection in common with SAS, tracking cookies.
Revo Uninstaller Free - This software lets you safely uninstall any software on your computer with almost no traces left. It's a great alternative to Windows' built-in uninstaller.