Online malware scanner for Mac (external drives incl.)

Hi there, lately my Mac has been running very sluggishly, and I wondered if there is any way to check if my Mac has been infected with Malware using a free online scanner? I used to use the Trend Micro Housecall scanner. But when I went to their site and downloaded the Housecall app, it opens, but immediately crashes, and I have to Force Quit the app.

 

Malwarebytes works pretty good

 

Downloaded the free trial of Malwarebytes, and the scan is clear. So I guess I need to figure out if there's some other reason why my Mac is running slower lately and occasionally freezing.

 

Have you tried running Disk Utility??

 

A

Disk Utility says that everything is ok.
I may however have another suspect. I was part of a photographic project that required multiple artists/photographers/videographers to upload their materials to a shared Dropbox folder. And that means that because that shared folder has to reside on my drive that it takes up a whole lot of space. I'm wondering if there's still enough space left on my drive to allow apps to run smoothly, or if I need to consider finding a way to delete those shared dropbox files from my folder, without deleting them on anyone else, so I can free up a bunch of space.

 

Trend Micro HouseCall - https://www.trendmicro.com/en_us/forHome/products/housecall.html

Eset's Online Scanner - https://www.eset.com/int/home/online-scanner/

F-Secure Online Scanner - https://www.f-secure.com/en/web/home_global/online-scanner

 

I tried Housecall, and the scanner worked eventually, but the scan was only 30 seconds long or so. It obviously only did a very shallow scan, and only on the Mac HD. It didn't scan any of the portable drives attached to the Mac where all my important files are kepot.
The ESET scanner is an exe file so won't work, and the F-Secure link says it doesn't have an online scanner for Mac, and I didn't want to install F-Secure's software in case it causes a conflict with the Avast software already installed.