A Georgia mother and her two daughters logged onto Facebook from mobile phones last weekend and wound up in a startling place: Strangers’ accounts with full access to troves of private information. The glitch — the result of a routing problem at the family’s wireless carrier, AT&T — revealed a little known security flaw with far-reaching implications for everyone on the Internet, not just Facebook users. In each case, the Internet lost track of who was who, putting the women into the wrong accounts.
