UPDATE: According to npm Inc., the issue has been resolved. This gist will be updated with a link to the post-mortem once it's published. Please make sure to read the below explanation anyway, since there may still be a security impact for you.
UPDATE 2: An initial statement has been released, in which npm Inc. states that there has been no security impact. A full post-mortem is said to be forthcoming, and will be added here when it's published.
UPDATE 3: The full postmortem has been published, including a list of affected packages.
There's currently a known issue affecting the NPM registry, making certain packages impossible to install. You may see an error message indicating that a package doesn't exist, or that the registry is down. More details can be found [here](https