Adware has been hijacking browsers and leading users to specific sites for money. Many of our clients believe they have a virus on their Macs. To clarify, I am reposting an article from AdwareMedic which is now MalwareBytes.

From AdwareMedic:
What is adware and where does it come from?
Adware is unwanted software that uses sneaky and dishonest methods to get installed on your computer, and then changes the behavior of your web browser. Once installed, it does things like injecting advertisements into web pages, causing pop-up windows or tabs to open to advertising sites, and changing your home page and/or search engine.
Where does it come from?
The short answer: from an installer for some app you were tricked into downloading from an unsavory site. This may be a site like Download.comor Softonic, or a site offering streaming of “free” videos, or from a piracy site or torrent, or something else similar.
Download this FREE utility to remove adware: