Many of us are aware that our online communications, including private e-mails and data typed into Web sites, could potentially be “sniffed” from the air by some scoundrel nearby. (Software for the purpose is easily available on the Internet.) But it seems rather unlikely, and we don’t know what to do about it anyway. So we surf and pray — and maybe take the advice often offered by security experts to avoid shopping or banking online during these moments. But increasingly there is something we can do about it….