For a website like AshleyMadison.com that prides itself on secrecy and anonymity, a breach like this can be catastrophic. The site’s subscribers pay to have access to other married people looking to have affairs. They all, presumably, felt that their private information was safe. “The quick answer is: not that safe,” says Dr. Michael Sulmeyer, the director of the Cyber Security Initiative at Harvard’s John F. Kennedy School of Government’s Belfer Center.He says Ashley Madison’s clients know now the truth of the web: everything is hackable.“Largely, you should not have an expectation of ultimate security and privacy,” Sulmeyer explains. “And...