A friend sent an email to me and a slew of others this week, using Gmail, that warned against opening any email that might arrive from her Hotmail account, which had been hacked. I don’t know what can happen if you open a hacked email, and I don’t plan to find out, but I do know something about my friend that she hadn’t intended: the email addresses — and many of the names — of her friends, acquaintances, and business connections, some 350 of them.