The r.a9g.io address belongs to a dubious search engine. Nothing wrong so far but this unfamiliar address was seen being opened automatically by the users' Web browser. This behavior is normally caused by a browser hijacker application that has managed to sneak its way into the user's Mac system without being noticed. Indeed, due to their intrusive actions, browser hijackers are not being distributed via the typical channels. Instead, they rely mostly on underhanded and deceptive tactics that mask their installation. One of the most widely used methods is called bundling. As such, these applications also are classified as PUPs (Potentially Unwanted Programs).
The main purpose of a browser hijacker is to drive as much artificial traffic as possible towards a promoted address. That is why the r.a9g.io page will be set as the affected browser's new homepage, new tab page and the default search engine. Users should keep in mind that fake engines generally cannot produce any meaningful search results. They either redirect to a legitimate engine or show low-quality results filled with ad links.
Another aspect that is often observed in browser hijackers and PUPs is that these applications spy on the user's browsing activities. Various data could be tracked, stored in a file, and then transmitted to a remote server. The acquired data can then be exploited to run a targeted advertising campaign or potentially be sold to any interested third parties.