Disable all sharing services (file, iTunes, etc) and if you do transactions on websites with passwords you care about make sure they are secure (https://) sites. This also includes email; if it is not encrypted (via SSL) your password is liable to be transmitted in plaintext, which may be picked up by someone running a packet sniffer on the same network.
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The opposite of a fact is falsehood, but the opposite of one profound truth may very well be another profound truth. - Niels Bohr
