There are several symptoms to look for when this particular threat and also unwanted apps in general are active:
Symptom #1: Your computer may become slow and has poor performance in general.
Symtpom #2: You have toolbars, add-ons or extensions on your web browsers that you don't remember adding.
Symptom #3: You see all types of ads, like ad-supported search results, pop-ups and redirects to randomly appear.
Symptom #4: You see installed apps on your Mac running automatically and you do not remember installing them.
Symptom #5: You see suspicious processes running in your Task Manager.
If you see one or more of those symptoms, then security experts reccomend that you check your computer for viruses.