“Having email addresses by itself is not much of a threat: people give them out all the time, and spammers can and do guess them easily,” said Eugene Spafford, executive director of the Center for Education and Research in Information Assurance and Security at Purdue University.

“It is more an issue if you can pair addresses with places of employment, such as government agencies,” he added. “Then it becomes possible to collect further information, and perhaps get a toehold into Google, Bing or other information sources.”