1. Gmail: Detecting suspicious account activity. http://googleonlinesecurity.blogspot.com/2010/03/detecting-suspicious-account-activity.html. Gmail: Detecting suspicious account activity. http://googleonlinesecurity.blogspot.com/2010/03/detecting-suspicious-account-activity.html.
2. NIST e-Handbook of statistical methods. http://www.itl.nist.gov/div898/handbook/. NIST e-Handbook of statistical methods. http://www.itl.nist.gov/div898/handbook/.
3. Yahoo: "on-demand" password. http://yahoo.tumblr.com/post/113708272894/a-new-simple-way-to-log-in. Yahoo: "on-demand" password. http://yahoo.tumblr.com/post/113708272894/a-new-simple-way-to-log-in.
4. The Cyberwire: Breaking news from RSA. April 2015. http://thecyberwire.com/issues/issues2015/April/CyberWire_2015_04_21.html. The Cyberwire: Breaking news from RSA. April 2015. http://thecyberwire.com/issues/issues2015/April/CyberWire_2015_04_21.html.