NSA Cyber Weapons Defense Tool is a free program which checks that your PC is protected from vulnerabilities relating to the leaked National Security Agency hacking tools. The most famous of these is EternalBlue, used by the WannaCry ransomware to infect hundreds of thousands of PCs, but there are many others.
The program is very simple. It looks at your installed Windows patches, checks to see if they include the releases Microsoft made for the NSA exploits, and warns you if any are missing.
If there's a problem, clicking the Fix button installs the missing updates.
You could do this already by running Windows Update on your own PC, of course. The sole advantage of NSA Cyber Weapons Defense Tool is that it has the patches included already, so works offline.
NSA Cyber Weapons Defense Tool doesn't reliably detect missing patches. We ran it on a fully-updated PC and it said we weren't protected against ten exploits: wrong. Our best guess is that it doesn't recognise all the possible Windows patches (they can be rolled up in different files, so it's harder to detect than you might expect).
We're also not happy about the principle of getting Windows updates from a third-party.
The tool's ability to run and fix PCs offline might be useful, but for the most part you're much better off updating Windows via the standard route. If you're missing the EternalBlue and related patches, you're probably missing others, too, and NSA Cyber Weapons Defense Tool can't help with that.