I walked through some tips for removing it here, but to avoid it in the future, know that it’s always best to check for updates to Flash, for example, through System Preferences rather than trusting that a browser pop-up you’ve seen is legitimate. You click through the prompts to install it (because you’re a good little Apple user, and you always stay up to date!), and suddenly, you’ve got a new homepage. You’re on a webpage, let’s say, and you get a notice that you need to update Adobe Flash.
A common cause of adware these days is nefarious browser pop-ups.