Yep. When more than one person uses a single computer, each should definitely log out when leaving the website. Otherwise, the last person's logon account (AND password!) is in use. Deleting cookies will also work, but then you have to log in at every web site you usually visit. That's not so bad, but more complicated. If it's only 2-3 people who trust each other, logging out will suffice.
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'..when you look long into an abyss, the abyss also looks into you.' - Nietzsche