use their unistaller first. then because it leaves behind (and possibly others I did not find in /var/ root directories)..
download findanyfile.app (Mac approved developer)
search for all files on your startup drive that contain com.piriform.ccleaner (make sure invisible items are shown)
select those and right click/contextual menu, move to trash OR delete immediately. all done. NEVER will install this app again, ever. it runs all the time in the background and auto starts without anyway to disable it. I want to use it when I choose to; also a privacy invader. bad app.