Hi,
Sciccors. Welcome to AppleNova!
For context, I have been the senior salesman at MacLife in Boise for 15+ years, and regularly deal with the type of issue you are having.
First,
You do not have a virus, you have malware. Second, Knowing what OS you are on will help.
Before you go to any great lengths, try this:
1) Download
Malwarebytes and
run it on your computer. You will need to give it full disk access (follow the instructions).
2) If Malwarebytes does not automatically restart your machine, then make sure you restart.
3) After restarting, look in System Preferences for "Profiles". If there are any profiles in there (and you didn't add them) delete them.
4) Come back and tell us how things went. There may be some items in your
LaunchDeamons and
LaunchAgents folders, or
Startup Items, which are all somewhat hidden. If the problem persist I'll guide you through that, as well as some additional cleanup items.
A full system wipe may be way overkill. Browser hijackers are actually easy to remove once you know what to do.
P.S. Please learn to avoid those "Adobe Flash Player is out of date" messages. You most likely clicked on one of those and inadvertently installed Safe Finder.
P.P.S. The most likely reasons the problem is returning for the other person from a clean install is that either A) the install is followed by a Time Machine restore, which would put the issue back onto the machine along with all the other files that were backed up; or B) the person is repeating the same mistake (i.e. getting tricked into "updating Adobe Flash" which, by the way, is a discontinued product no longer in need of updating.)