Online advertising is a form of advertising that uses the Internet and World Wide Web. Apart from it being accessible from around the world via the Internet, it is also usually instantaneous; conventional, printed advertising has a delay time due to printing. With recent years, online advertising has evolved and now has many variations. Listed below are a few variations most frequently encountered.

Email advertising

An increasingly used variation of online advertising, advertisers make use of mailing lists obtained via website memberships, surveys, or forms. However, an "opt-out" option should be included to make it legitimate, as well as differentiate it from Spam. This method of advertising is generally not very well received by its recipients as most users will treat advertising email as spam, regardless of whether it is a legitimate advertisement or not.

Rich media advertising

Rich media advertising is becoming extremely popular, and a majority of these are generally done using Adobe Flash. This variation makes use of graphics, color, page layout, animation, and other various elements to attract attention. Some users might consider these ads a nuisance as they can distract attention from the actual content of the page being viewed. Some popular examples of rich media advertising are banner ads (static or animated ads with a fixed height and width), "fake" banners (banners that appear on the user's screen usually as a dialog box with buttons that simulate an alert or error message), pop-ups (a new window which "pops out" suddenly in front of the current one and displays an advertisement or entire webpage) and video ads (similar to banner ads but displays actual video clips instead of a static or animated image).

Contextual advertising

One of the most popular variation of online advertising, it also usually gives the highest Return On Investment (ROI), can reach out to a wider audience, almost instantaneous, and is the most available and affordable. Contextual advertising are usually ads that contain only text or static pictures.

Malicious ads or Malware

Malware is an advertising variation that is considered unethical by many, and may even be illegal. This variation of advertising include having multiple pop-ups appear instantaneously and unseen applications which may alter system settings. These applications are labeled spyware or adware. They usually go under the pretense of displaying the weather or a "harmless" looking search bar. Some programs are even Trojans, which are difficult to uninstall or get rid of, and are potentially harmful to computer systems. They may retrieve sensitive information like usernames and passwords.

Dean currently works in an IT firm, and writes short articles when the bug bites him.

A few popular sites that provide free services for contextual ads would be USFreeads.com, Kijiji.com and Ablewise.com Free Classifieds.