Unfortunately, as you might expect, the answer is complicated. I actually have an answer that will totally solve this problem in under 3 minutes. Because because I wrote the app, I can't give you a link to it here in the forums.
I can't recommend any 3rd party "security" apps. There are so many scams out there.
If you don't want to take the trouble to do a Google search or wait 3 minutes, you can manually look in one of the 3 folders listed below:
/Library/LaunchDaemons
/Library/LaunchAgents
<your home directory> /Library/LaunchAgents
That last one is the most likely. In Finder, choose "Go to Folder" from the "Go" menu. Enter the following in the dialog:
~/Library/LaunchAgents
and press enter. Hopefully it works. Depending on your operating system and a thousand other things, it might not.
Repeat for the other directories.
Look for any file that doesn't have a recognizable word and delete it. If it says "Microsoft", "adobe" or any other trademarked name that you recognize, don't delete it. Strangely enough, malware authors have great respect for trademark law.