Once in Activity Monitor, look for any processes that have names related to Yahoo or are using more CPU than usual (this could be an indication of malicious activity).

Source: https://www.devicemag.com/get-rid-of-yahoo-on-safari/

Once the Activity Monitor is open, search for ‘Finder' and select it from the list of processes.

Source: https://www.devicemag.com/how-to-quit-finder-on-mac/

To double-check this, you can use the Activity Monitor app to view how long each file is taking to transfer.

Source: https://www.devicemag.com/how-long-does-it-take-to-backup-a-macbook-pro/

To find out what is slowing down your Mac, you can open Activity Monitor which can be found by clicking Go in the macOS menu bar, choosing Utilities and selecting Activity Monitor.

Source: https://www.devicemag.com/check-mac-system-performance/

To find out what is slowing down your Mac, you can open Activity Monitor which can be found by clicking Go in the macOS menu bar, choosing Utilities and selecting Activity Monitor.

Source: https://www.devicemag.com/check-mac-system-performance/

You should also check Activity Monitor for any processes related to the virus.

Source: https://www.devicemag.com/get-rid-of-yahoo-on-safari/