What are extensions?
Extensions are small software programs that customize the browsing experience. They enable users to tailor Chrome functionality and behavior to individual needs or preferences. An extension must fulfill a single purpose that is narrowly defined and easy to understand. A single extension can include multiple components and a range of functionality, as long as everything contributes towards a common purpose.
User interfaces should be minimal and have intent. Extensions can range from a simple icon, such as the Google Mail Checker extension shown on the right, to overriding an entire page.
There are some developers that create extensions that modify the behavior of Chrome in a negative way. For example, adware developers may install Chrome extensions without your permission that inject advertisements on to web pages that you are viewing, change your search provider to a site under their control, change the new tab page, or hijack your home page.
You can see an example of a malicious extension called Search-NewTab that injects advertisements in the image below. It goes without saying that you should always remove malicious Google Chrome extensions when you encounter them.
Example of a Malicious Chrome Extension