Okay, time for true confessions. Ever looked up an ex on facebook? You might call checking in. Others might call it surveillance. Whatever you call it, a third of us do it. Now, of course, there are... See More
Okay, time for true confessions. Ever looked up an ex on facebook? You might call checking in. Others might call it surveillance. Whatever you call it, a third of us do it. Now, of course, there are always people who want to get a little too up close and personal to celebrities, but what about what is being called social stalking? Looking up someone who may have dumped you, have you done it? You may have and not even know it. Take our test and see if you are a little bit stalker. Here's jay schadler. Right here. Reporter: In our celebrity-drenched culture, it's a sad but not altogether surprising fact that sometimes fascination warps into obsession. This man kept a video diary as he constructed a bomb to send to pop singer bjork. Look at this beautiful face. I'm just going to have to kill her. Right to that frightening stalking with miley cyrus. Reporter: Just this past month, police responded to a 911 call of a prowler at the hollywood home of miley cyrus. Keep your hands up. Walk towards us. Reporter: Now, cyrus has been the target of stalkers before but this time the fellow actually insists he's married to the starlet. I am. Reporter: He has since pled not guilty to trespassing. Back in january, a fan-turned-stalker breaks into mila kunis' los angeles house. She isn't there. But the police say the stalker, named stuart dunn, proceeds to call her place home for the next two weeks! The police are telling us they're calling him a stalker. But it's a dangerous stalker because anybody who breaks into your house, you know, is not just standing there trying to get an autograph. Reporter: A few months later the same guy shows up three days in a row at kunis' beverly hills gym. Kunis is terrified. He later pleads not guilty to stalking her. The paradox, of course, is that celebrities want attention -- just not the freaky kind. But now, the new social media universe only complicates matters. Suddenly, the mundane musings of your favoritxpstar elode on your twitter account. We're going out tonight. It's going down. Reporter: Pictures of how taylor swift spends her free time are on instagram. Katy perry details her night out on twitter and the kardashians, well, some might say they're paractically "stalking" us! Someone, somewhere is always watching. Today, news broke that roger federer has become the target of an online stalker. Social media has thrown privacy into a tailspin. Reporter: Psychologist, seth meyers. There's so much information that people are able to get their hands on that it can really take the fascination to a level that becomes destructive. Reporter: Occasionally, social media becomes the method for a true stalker's madness. And the targets are not just celebrities anymore: Imagine you're home alone on facebook when suddenly a death threat message appears. This isn't a movie plot, and 17-year-old caylee bogges is not a celebrity. He said I had two weeks left to live before he brought me from point q "a" to point "b." Reporter: For months this summer, caylie received these horrifying and relentless threats from an anonymous online stalker. It was very nerve-racking all the time. I never went anywhere by myself. Reporter: Last month, police arrested 20-year-old craig wyatt jr. Through facebook, e-mails and cell phones, police say he had been haunting caylee and more than two dozen other women. Craig wyatt may have thought it was a joke. It wasn't a joke to these victims. They took if very seriously and so did we. Reporter: While wyatt's case is extreme, most of us understand the addictive quality of surfing social media. And it turns out, the internet's voyeuristic appeal can bring out a little bit of the stalker in all of us. In fact, facebook stalking is a growing trend. Many of us have done it. Flipping through photo albums and posts never leaving a trace and all the while finding out the intimate details of our ex's lives. Just ask tracy clark-flory, a writer for "salon." I found myself newly single and feeling a bit sorry for myself. Reporter: So she pops onto flickr to check up on her ex-boyfriend. I saw a self portrait that he'd taken of himself, and it showed him wearing a wedding ring. Reporter: Ouch. Yes, exactly. Reporter: But unable to stop looking, tracey ultimately finds herself peeking in on his wedding pictures. It was very surreal. It's one thing to hear about an ex getting married. It's a totally different thing to be a virtual bystander to the actual ceremony. Reporter: That fits neatly with the findings of a recent study suggesting this kind of online stalking "obstructs the process of healing and moving on from a past relationship" or as tracey puts it -- it makes it impossible to actually truly disconnect sometimes from people you'd rather be disconnected from. Reporter: In the end, the internet remains a remarkable and sometimes risky tangle of connections. Best advice, if you go spinning across the web, beware of spiders. ♪
This transcript has been automatically generated and may not be 100% accurate.