Back in 2013, hackers breached a secret corporate database that was used to track bugs in its own software. It happened at a time when Facebook, Apple and Twitter were hacked; at the time, Microsoft merely confirmed that they, too, had been targeted. But they did not reveal the seriousness of the attack.

In Reuters’ special report, Joseph Menn puts it in perspective this way: “The database contained descriptions of critical and unfixed vulnerabilities in some of the most widely used software in the world, including the Windows operating system. Spies for governments around the globe and other hackers covet such information because it shows them how to create tools for electronic break-ins.”

While it’s believed that the flaws were fixed shortly after the cyberattack, former employees and US officials expressed concern that the data could have been used to launch widespread attacks on government and corporate networks.

Read the full story at Reuters.