Just because you're paranoid doesn't mean you're wrong. Many companies do business on the internet and want to track what you, the user, are doing. Some of these companies have your interests in mind when they do this, for example ebay tells you about the last items you looked at. This is convenient to you, but it also helps the business interests of the web site. That's the way business works, though, right? You give them a little information about what you're interested in. In return, they make it easier for you to find those items, but they also learn how to better advertise to you.
Business works fine when there's give and take and everything is done with the customer's clear consent. Some companies on the web, however, aren't up-front about their intentions. Some of the techniques applied by unscrupulous advertisers include using pop-up ads on sites that they don't own, using pop-up ads when you're not even online, or hijacking your web browser to force you to visit their site (these are often disguised as an error message with a search option). These advertisers will also attempt to get software on to your computer that will furthur their efforts. This software is generically called "Spyware" but has many other names as well.
Too often, when things show up on their computers, users blame their browsing habits. But there's no easy way to tell which sites or which software will come with unwanted side-effects. You can expect that at some point, something's going to slip by and wind up on your computer. Run software like "Spybot, Search and Destroy" or "Adaware." These tools are both free and can both pick up a very wide range of unwelcome intruders.
If you can't shake that feeling you're being watched, call us up. Late Night PC Service can help you figure out why you get so many pop-ups, why your web browser won't browse, or what that little program is that wasn't there before.