Windows Security Software Flaw Used in Ransomware Attacks

Hackers discovered and exploited a serious security flaw in Microsoft Defender, the built-in antivirus and security software that comes with Windows computers.

This vulnerability, tracked as CVE-2026-33825 (an industry tracking number for this software flaw), was used by criminals to launch ransomware attacks. Ransomware is malicious software that locks your files and demands payment to unlock them. The attacks happened before Microsoft had a chance to release a patch to fix the problem, which is known as a zero-day (a newly discovered software flaw with no fix yet) exploit.

This vulnerability affects people and organizations using Windows computers with Microsoft Defender.

If you use a Windows PC at home or work, your system was potentially vulnerable to this attack method.

The good news is that Microsoft has now released security patches to fix this problem. However, if your computer was targeted before the patch was available, your files may have been encrypted by ransomware. Take these actions right away:

1. Update your Windows computer immediately by going to Settings, then Windows Update, and clicking Check for Updates. Install all available updates.
2. Make sure Windows Defender or your antivirus software is running and up to date.
3. If you notice any unusual files, locked documents, or ransom messages on your computer, disconnect from the internet immediately and contact a computer professional.
4. Do not pay any ransom demands without first consulting with law enforcement or a cybersecurity professional. Protect yourself in the future by enabling automatic Windows updates so your computer receives security patches as soon as they become available. Regularly back up your important files to an external hard drive or cloud service that is not always connected to your computer. This way, if ransomware strikes, you can restore your files without paying criminals. Keep your antivirus software active and perform regular scans of your system.