Adware is designed to deliver advertisements to the user.

The most common form of adware is browser hijackers. You experience ads while surfing and often mistake the cause as coming from the website you are visiting. Some adware programs change pieces of text on the site you are visiting.

One of the more common forms of adware will change the browser extensions/add-ons.



Then there are adware programs that change your start-page, search-engine or even by changing the shortcuts on your computer, which then will open your browser(s).

Some of the most common forms of adware are the following:

Pop-ups: an ad-created new browser window or tab that has focus( i.e. shows up in the foreground).

Pop-unders: as above, only the window stays in the background or the tab is without focus,

DNS-hijack: changes the servers that handle your Domain Name System that “translates” the domain-name into a physical address. So, effectively, it sends you to a different site than the one you requested.

Proxy: adds an extra step between the surfer and the destination. They can be used to alter content or redirect the user.

Hosts: the hosts file is a list of domains coupled with IP addresses. Since it preceeds DNS it can be used as a hijacker, and has been known to be abused to block access to computer security related sites.

Text popups: a link that opens a popup box containing advertisements, usually prompted by a mouse-over.

Source: MalwareBytes