Pop-up windows appear from nowhere when surfing the web, obscuring the website you want to look at with adverts. Some are merely annoying, but others contain material that is inappropriate for many users. Most modern web browsers include a built-in pop-up blocker that stops them appearing.

Users of Internet Explorer 7 will find that the pop-up blocker is enabled by default. To customise it, click on the Tools button, followed by Pop-up Blocker, and then Pop-up Blocker Settings. At the bottom of the dialogue box, it is possible to configure how stringent the blocker should be, and there is the option to allow legitimate pop-ups from trusted sites.

This can help to combat pop-ups hidden in web pages, but some pop-ups can be a symptom of a spyware infection. A program called Ad-Aware can automatically block pop-ups that originate from a number of well-known sources.