Since this system belonged to someone else, best you can do as format and do a clean install of the things you want to have on it. When removing applications, most of them leave some things behind “poluting” the system.

If you don’t want/can’t do that. I suggest you have a look at the page in my signature to clean your system from the malware.

And browse your system looking for temp files/folders, empty folders and such and remove them manually.