OSX/QHostWBA is a Trojan that masquerades as a Flash Player installer to install malware that manipulates the computer's hosts file to redirect Google sites to visually similar websites that serve additional content and ads [1]. It was the first signature added with new daily update system [2].

References:

1. https://www.f-secure.com/weblog/archives/00002206.html
2. https://www.macrumors.com/2011/08/12/apple-updates-anti-malware-definitions-to-address-fake-flash-player-trojan/