How to find and kill an installer that autostarts at boot time
Besides the Login Items (Open the Users &amp; Groups pane of System Preferences),
try this.

In Terminal, type 

ls ~/Library/LaunchAgents


You will see your "personal" launch agents.

To see all the currently loaded agents, type this:

launchctl list


If you can identify the one you don't want, use the unload option:

launchctl unload ~/Library/LaunchAgents/whateverItIsYouWantToUnload