It sounds like something Illustrator related might be in the LogIn items for your account. I accidentally added Safari once because I accidentally chose the "Open at Login" option while it was in the Dock.
Go to system Preferences and upon the "Accounts" preference pane. Find the account that is giving you problems and click the "Login Items" tab. If you find Illustrator there you can delete it by selecting it and then hitting the "-" button. You will be asked for an administrator password at some point in this process.
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