SAN FRANCISCO—Hackers from Iran are suspected of swiping authentication data from a US computer security firm in an attempt to impersonate popular Google or Yahoo! sites. "The incident got close to, but was not quite, an Internet-wide security meltdown," Electronic Frontier Foundation senior staff technologist Peter Eckersley said in a message posted at the group's website. Hackers using computers with addresses in Iran posed as a European affiliate of New Jersey-based Comodo on March 15 to get digital certificates allowing the creation of imitation Google, Yahoo!, Microsoft or Skype log-in pages. "The attacker was well prepared and knew in advance...