I know you are not running Windows, and most likely anything I could think of you have already tried... but I had a similar experience a couple of months ago with a web search-bot called General Crawler. It installed copies of its executable files 'way deep down inside my directory tree, and then put a "trigger" in my system registry so that even though I had run the "Uninstall" routine, the trigger would re-install it upon reboot.

Your Macintosh OS hasn't anything like the Windows registry, but could something of the same general idea be gong on with your system?

tanstaafl.