The first thing I think of when stalking comes to mind today is actually cyberstalking. So, I think we're all probably guilty of checking someone out online. I mean, who hasn't googled an ex at some point? Some people call this "stalking", often in an off-hand kind of humorous way.
But there's a definite line to be crossed where the use of technology is used to harass and instill fear into the person being stalked. According to the dictionary definition, cyberstalking is "the repeated use of electronic communications to harass or frighten someone, for example by sending threatening e-mails." Of course, people are creative. There's always new ways they can come up with to cyberstalk. But, I'd say, the underlying problem is the fear and harassment that can really harm someone and do some serious psychological damage. Anyhow, if you, or someone you know, if facing problems with this, then don't hesitate to seek help! A few places you might want to look into: