advice on web advertising
Many Web sites carry advertising. The problem for Web users is that they have no choice whether they wish to see the adverts or not. Being graphical, adverts can add considerably to download times, while some users find them distracting. Adverts often collect information about your browsing habits without your knowledge. Malicious adverts are sometimes inserted into compromised, genuine Web sites in order to deliver viruses to users.
There are several products which block adverts. They may also filter associated components (e.g. cookies and web bugs) which can compromise your privacy. They are installed as an add-on or extension to your browser. A well-reputed example is AdBlock, not to be confused with another product called Adblock Plus.
Another product is Ghostery. Ghostery is not an ad blocker per se. Its main function is to block all those components on a Web page that seek to track the user's behaviour, including adverts themselves.
Adware and spyware
Many computers have had programs downloaded on to them without their owner's knowledge. These programs are known as adware or spyware since their purpose is to gather information about your Web browsing habits so that you can be fed with targetted adverts over the Web (or possibly via junk e-mail). They are usually installed silently as a result of you downloading and installing another program, invariably a free one. Unlike viruses, they represent more of a threat to your privacy than to your computer's security. However, the boundaries between adware, spyware, viruses and junk e-mail (spam) are not rigid and they are increasingly used in combination.