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Do ensure you protect your usernames & passwords when you log on. I know it's obvious, but it's easy to forget.
It's also a wise idea to change your password every so often, too.
how does one secure it?
Use your own laptop. Public computers, in my experience, are usually unpatched Windows machines running every toolbar on the market, stuffed full of spyware and trojans. https is no good, because someone could simply be running a keystroke logger on the machine to pick up passwords, credit card numbers, etc. - there have been a number of cases of this.
Public computers are simply not secure, and not secureable. The only way you might be able to use one is if you can boot it with something like a Knoppix bootable CD, then you're not running their installed programs at all - however, it is rare that they would allow this.