WTF?!

Can someone, for the love of Christ, please tell me how a blogger knows who's been reading their blog?

I ran across a post by someone who was complaining about "lurkers," whom she defines as people who read her blog but don't leave comments. How the hell does she know who's reading the blog if they don't leave comments? She seems to know not only that these lurkers ping the blog, but what they read and whether it includes reading the comments. She even mentioned one by name and listed his IP address. How in the name of God does someone determine this? She knew the guy's sign-on name, his IP address, and what he reads when he goes to her blog.

In the five million comments she receives to every blog she posts, a whole freaking bunch of people confessed to having "lurkers" on their blogs and what they did about it. WTF? Am I the only person out there who doesn't know how to do this? Of course none mentioned HOW, only what they did about it. Is being a "lurker" a bad thing? I read many blogs, but I don't always leave comments. Is that the same as coming to your house to peer into your bedroom window without tapping on the glass to say hello?

Can anyone out there help me?