As much as Genieo Innovation dislikes the term PUP (potentially unwanted program), that's probably an appropriate label.
Genieo is designed to generate a dynamic and personalised home page based on the user's browsing activity. According to the company "its entire mapping and profiling process is performed solely on your computer - unlike other personalized homepages, which require interaction with web servers. This means your private data is always maintained on your own computer and is not registered or shared anywhere on the web."
Taking that assertion at face value, it all seems quite reasonable, especially as "Genieo is designed to automatically exclude any sensitive content, from displaying on your Homepage. [sic]"
A piece of software that pretends to be one thing (useful, fun, interesting, etc) while actually doing something that may be contrary to the user's interests is normally described as a Trojan Horse.
What's the motivation for the people behind these fake installers? That's not completely clear, but a reasonable guess is that they are taking advantage of a pay-per-install scheme.
The other issue is that Genieo is installed alongside some otherwise legitimate applications. Genieo Innovation has a second operation called InstallMac, which pays developers each time their software is installed in return for bundling the Genieo software.
There's nothing inherently wrong with that, providing the user is clearly advised of what's happening and is given an opportunity to opt out - or better still, has to opt in.
Page 2: How to clean up Genieo.
Typical computer users have demonstrated that they like stuff they don't have to pay for upfront. Look at the way games in particular are moving towards a model where you can start playing for free, but once you're hooked you'll need to make in-game purchases.
And some developers have found they get more revenue from free apps with in-app advertising than they do by selling an ad-free version.
The problem with Genieo is that it affects the target system generally - not just the application it's bundled with - and also that a large proportion of recipients seem to think they weren't given adequate warning of its presence so they could prevent its installation.
Furthermore, there are reports that the InstallMac 'uninstaller' actually installs Genieo components if they are not already present.
Consequently, various security products detect the Genieo adware, including Avast (since May 2013), Intego (since May 2013), and Sophos (since January 2014).
Bitdefender also offers a free adware removal tool that "completely removes Genieo for Mac" - this apparently includes resetting browser search settings that are changed by Genieo.
You can also find instructions for manually installing Genieo at MacIssues.