Lessons from the Yahoo Breach.

• Position: CYBERSECURITY

When Yahoo recently announced that at least 500 million Yahoo users' account information was stolen by hackers in 2014, the biggest surprise was not that it was the largest data breach to date, but that it took Yahoo nearly two years to discover and make it public.

In a statement, Yahoo said user information--including names, e-mail addresses, telephone numbers, birth dates, encrypted passwords, and, in some cases, security questions--was compromised in 2014 by what it believes was a "state-sponsored actor."

According to the New York Times, Yahoo is one of the Internet's busiest sites, with one billion monthly users. Many users have used it to build their digital identities, from their bank accounts to photo albums and even medical data.

Upon discovering the breach, Yahoo instructed users to change their passwords and remain vigilant over all of their online accounts. Yahoo said it was working with law enforcement and encouraged people to change the security on other online accounts and monitor those accounts for suspicious activity as well.

Yahoo said it learned of the data breach this past summer after hackers posted to underground forums and online marketplaces what they claimed was stolen Yahoo data, the Times reported. A Yahoo security team was unable to verify those claims, but eventually found a breach by what the team believes was a...