Did you ever wonder about those ads on a Web site that specifically mention your hometown? You also see ads for products you looked at online, but never purchased. And some online ads seem frighteningly tailored to your likes.

By simply visiting a Web site, you reveal more than you probably realize. They know where you're located and other sites you've visited. Sites can even learn intimate details about you, like medical conditions.

Many sites gather information about your machine. They can tweak design elements for your visit. If your Internet speed is slow, for example, they can automatically change a video’s resolution.

See for yourself what you reveal by simply visiting a Web site. Visit my Privacy Check page now at http://www.komando.com/privacycheck. This page is for demonstration purposes only; no information about you or your machine is saved.

Software and IP address

So, for starters, sites know what browser and operating system you use. They can also see the language you speak. A malicious site can target specific vulnerabilities in your browser.

Sites also know your IP address. Your IP address identifies your computer on the Internet. It reveals your Internet provider. Undoubtedly, you've seen ads tailored for your location. Now you know why.