Disgruntled researcher leaks Defender zero-days, leaving Windows users exposed
A disgruntled security researcher leaked three Microsoft Defender zero-days—BlueHammer, RedSun and UnDefend—exposing over a billion Windows users; BlueHammer has been patched in the April 2026 updates, while RedSun and UnDefend remain unpatched but are already being exploited in the wild. Users should install the April 2026 security updates now and monitor for future patches, with additional antivirus protection to bolster defenses.