ON THIS LINK

However like dark matter, dark users are observable due to their effects on the rest of the universe. If a dark user comments on a stream entry, I can see that comment. More importantly, I can see their user-ID, and I can generate a URL to a page that will contain their name. I can then watch for their activities elsewhere. Granted, I can't directly search for their activity, but I can observe their effects on my friends. For want of a better term, I've been calling this "dark stalking".