LAS VEGAS, NEV. — iPhones and other mobile devices with wireless access were among the top contributors to this year’s “Wall of Sheep,” a public shaming exercise debuting at the Black Hat security conference in Las Vegas this week that aims to educate people about the dangers of sending e-mail and other online communications over open wireless networks. Conference organizers issued a clear warning to attendees: If you check your e-mail or communicate using the ubiquitous conference wireless network, be sure to do so over an encrypted connection (https:// versus http://). Otherwise, your credentials will be projected onto a wall where everyone will ridicule your seeming inability to grasp a fundamental tenet of online security. Apparently, a fair number of the most well-trained security professionals ignored this advice. The team responsible for monitoring the Black Hat wireless network posted more than 30 sets of credentials, many from individuals who had